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Anyone here familiar with so-called 'zipper noise' in audio remote/automation level control applications ?

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Eeyore

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Oct 24, 2008, 7:46:44 PM10/24/08
to
If so there's a quick question I'd like to run by you.

Graham

Robert Baer

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Oct 24, 2008, 10:26:54 PM10/24/08
to
Eeyore wrote:
> If so there's a quick question I'd like to run by you.
>
> Graham
>
The first digital pots were rather bad; two sources (1) not many
steps = large step function in "analog" output and (2) large gate
capacitance coupling on/off step voltage to source/drain.
The newer ones are better, but i would use a scope synched with the
digital command pulse, tie each end of pot to resistor to ground where
resistance is equal to that of pot; scope probe to "tap" / "output".
Should give you an idea as to how good/bad that coupling is.

Paul Probert

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Oct 24, 2008, 9:50:06 PM10/24/08
to
Eeyore wrote:
> If so there's a quick question I'd like to run by you.
>
> Graham
>
Are you talking about "motorboating", which you get by biasing a single
sided opamp audio circuit by just resistively dividing the power rail?
When I turn on a circuit I built that way it does sound like a zipper,
ie a run of pulses chirping upward in frequency.

Paul

Guy Macon

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Oct 25, 2008, 12:33:43 AM10/25/08
to


Eeyore wrote:

>Anyone here familiar with so-called 'zipper noise' in audio
>remote/automation level control applications ?

I am very familiar with it. The usual quick and dirty fixes are:

[1] Use lots of bits / high resolution.

[2] Slew-rate limit the fader so that is someone slams
the pot from bottom to top it doesn't skip too many steps.
This decreases zipper noise at the cost of increasing lag.

[3] If it's a gain applied to a analog su=ignal, Do the
actual gain switching at zero crossing. )Note: may conflict
with [2])

[3] If the entire signal chain is digital, de-zipper the
gain change by interpolating a bunch of small steps in software
between the larger steps from the fader hardware.

[4] Watch the gain structure so the system isn't using
the bottom 1% of the fader and following it with high gain
elsewhere.

BTW, if you are doing wolume control in a Windows program, read this:
http://blogs.msdn.com/larryosterman/archive/2005/06/16/429820.aspx

>If so there's a quick question I'd like to run by you.

Glad to help any way I can...

--
Guy Macon
<http://www.GuyMacon.com/>

Phil Allison

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Oct 25, 2008, 12:44:22 AM10/25/08
to

"Eeysore Red Hot Fuckwit "

>
> If so there's a quick question I'd like to run by you.
>


** GIANT HUH ???????????

So - this demented, stuffed donkey wants someone to declare they already
know the answer to a question he has not yet posted.

Don't' play any such stupid games with this ridiculous TROLL.

.... Phil


Eeyore

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Oct 25, 2008, 1:39:38 AM10/25/08
to

Paul Probert wrote:

> Eeyore wrote:
> > If so there's a quick question I'd like to run by you.
> >

> Are you talking about "motorboating", which you get by biasing a single
> sided opamp audio circuit by just resistively dividing the power rail?
> When I turn on a circuit I built that way it does sound like a zipper,
> ie a run of pulses chirping upward in frequency.

You're referring to power rail modulation classicly caused by insuffient
local supply decoupling I take it ?

Zipper noise is another effect, essentially a fast series of 'Fourier
clicks' typically caused by a moderately rapid sequence of step gain
changes in audio level in a 'fade-out' for example, so called because it
sounds like the zip on your jeans or whatever. When using a VCA gain
element it can be 'smoothed' somewhat by RC filtering of the control
voltage but is inherent in DSP and can only be removed there by making the
step size very small and therefore all but inaudible.

Graham

Eeyore

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Oct 25, 2008, 1:47:24 AM10/25/08
to

Phil Allison wrote:

Phil's there a mathematical treatment of the analysis of this noise that I
believe may be sufficient to 'prove' that a TI chip, the PGA2310 would not be
suitable for automated / remote level control because of the limited number of
steps (256) even though they are only 0.5dB each. I suspect it may still
produce zipper noise because the step size, although 0.5dB step despite
sounding small there are still only 256 of them (which is a classic number for
producing zipper noise) and TI are I suspect foolishly mis-promoting it in the
pro-audio market.

It would doubtless be fine for slow level changes but not fast ones.

Graham

Eeyore

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Oct 25, 2008, 1:50:41 AM10/25/08
to

Robert Baer wrote:

Shouldn't be a coupling noise in this case, the gain chip is from TI's BB
division who ought to know better. It's the step size that concerns me.

I did a simplistic calculation which suggested the transient zipper noise
involved with 0.5dB steps may be as bad as -20 ish dB which is absurdly
poor for the design in question.

Graham


Eeyore

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Oct 25, 2008, 1:51:54 AM10/25/08
to

Guy Macon wrote:

Sounds like you're my man. I've been up late so will explain later in
more detail.

Graham

Phil Allison

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Oct 25, 2008, 2:36:40 AM10/25/08
to

** Never heard timing the steps to coincide with zero crossings of the
signal ???

Standard practice is all but low end AV gear.

Read the data sheet - dickhead.

..... Phil

Martin Griffith

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Oct 25, 2008, 3:49:32 AM10/25/08
to

It's expensive, as well.They should have reduced to step size

Did something similar in the 80's, ended up with 2 multiplying dacs
with some soft FET switching, so you would update the off channel, do
a soft switch, say 1msec to the updated dac
Quite messy
I still like the alps motorised volume controls, (silly) but they
don't have a feedback/position sensor

martin

IanM

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Oct 25, 2008, 6:02:22 AM10/25/08
to
>
> BTW, if you are doing wolume control in a Windows program, read this:
> http://blogs.msdn.com/larryosterman/archive/2005/06/16/429820.aspx
>
Thanks for that, I now have a nice taper on my laptop volume control

Ian


Jan Panteltje

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Oct 25, 2008, 7:55:18 AM10/25/08
to
On a sunny day (Sat, 25 Oct 2008 06:39:38 +0100) it happened Eeyore
<rabbitsfriend...@hotmail.com> wrote in
<4902B11A...@hotmail.com>:

>You're referring to power rail modulation classicly caused by insuffient
>local supply decoupling I take it ?
>
>Zipper noise is another effect, essentially a fast series of 'Fourier
>clicks' typically caused by a moderately rapid sequence of step gain
>changes in audio level in a 'fade-out' for example, so called because it
>sounds like the zip on your jeans or whatever. When using a VCA gain
>element it can be 'smoothed' somewhat by RC filtering of the control
>voltage but is inherent in DSP and can only be removed there by making the
>step size very small and therefore all but inaudible.
>
>Graham

Hello Mr Rabbit

That what you call 'zipper noise', is familiar to me.
You find it for example in my sound blaster (EMU10) based sound card, when moving the slider.
Now a few interesting points:
This sound card also does zipper noise when silence, so you hear indeed
a zipper like noise when the slider moves.
So the design of the attenuator sucks (Hello Creative Labs).

So, first you should make sure changing attenuator steps (in hardware or software)
does not cause a signal by itself.

Second, and this is something I have only tested in a *light* related application,
perhaps you should, or could, switch amplitude only on the zero crossings of the audio
signal.
This would mean worst case for 20 Hz every 50 milli seconds,
So if the slider moved a lot in those 50 milli seconds, then you would have to move
a bit more at once, but during the zero crossing.
This does actually prevent higher harmonics switching noise.
I patent this solution hereby, and just because you insulted me and other people
in your previous rabbit posting, you own me 1000 Internet Credits for every
device you sell that uses my solution.

I am a bit surprised though that an audiophool genius like you cannot fix a simple
issue like that all by himself.

Greetings from
Dark Fader


Eeyore

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Oct 25, 2008, 11:17:13 AM10/25/08
to

Phil Allison wrote:

Yes.


> Standard practice is all but low end AV gear.
>
> Read the data sheet - dickhead.

And what happens when it times out eh ?

ZERO CROSSING DETECTION
The PGA2310 includes a zero crossing detection function
that can provide for noise-free level transitions. The
concept is to change gain settings on a zero crossing of the
input signal, thus minimizing audible glitches. This
function is enabled or disabled using the ZCEN input
(pin 1). When ZCEN is low, zero crossing detection is
disabled. When ZCEN is high, zero crossing detection will
be enabled.
The zero crossing detection takes effect with a change in
gain setting for a corresponding channel. The new gain
setting will not be latched until either two zero crossings
are detected, or a timeout period of 16ms has elapsed
without detecting two zero crossings. ****In the case of a
timeout, the new gain setting takes effect with no attempt
to minimize audible artifacts.****

Suggest you read the datasheet. Page 10

Graham

lang...@fonz.dk

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Oct 25, 2008, 11:18:30 AM10/25/08
to
On 25 Okt., 01:46, Eeyore <rabbitsfriendsandrelati...@hotmail.com>
wrote:

> If so there's a quick question I'd like to run by you.
>
> Graham

I have read an article about "gating" the update of level with zero
crossings
to eliminate it.

-Lasse

Eeyore

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Oct 25, 2008, 11:22:20 AM10/25/08
to

Martin Griffith wrote:

> Eeyore wrote:
> >Phil Allison wrote:
> >> "Eeysore Red Hot Fuckwit "
> >> >
> >> > If so there's a quick question I'd like to run by you.
> >>
> >> ** GIANT HUH ???????????
> >>
> >> So - this demented, stuffed donkey wants someone to declare they already
> >> know the answer to a question he has not yet posted.
> >>
> >> Don't' play any such stupid games with this ridiculous TROLL.
> >
> >Phil's there a mathematical treatment of the analysis of this noise that I
> >believe may be sufficient to 'prove' that a TI chip, the PGA2310 would not be
> >suitable for automated / remote level control because of the limited number of
> >steps (256) even though they are only 0.5dB each. I suspect it may still
> >produce zipper noise because the step size, although 0.5dB step despite
> >sounding small there are still only 256 of them (which is a classic number for
> >producing zipper noise) and TI are I suspect foolishly mis-promoting it in the
> >pro-audio market.
> >
> >It would doubtless be fine for slow level changes but not fast ones.
> >
> >Graham
> It's expensive, as well.They should have reduced to step size
>
> Did something similar in the 80's, ended up with 2 multiplying dacs
> with some soft FET switching, so you would update the off channel, do
> a soft switch, say 1msec to the updated dac
> Quite messy

I follow you and can quite believe it.


> I still like the alps motorised volume controls, (silly) but they
> don't have a feedback/position sensor

That's silly of them. In this case however the objective is to get a near perfectly
matched stereo (or multi-channel) volume control which is DC controlled (obviously
using an A-D) but I don't think the results will be adequate for pro-audio fades
etc. And it is *high-end* pro-audio.

Totally agree with your comment about the step size and it would have nice if they
soft switched in the PGA.

Graham

Eeyore

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Oct 25, 2008, 11:27:18 AM10/25/08
to

Jan Panteltje wrote:

Exactly the problem. 50ms is too slow. And the chip has a 16ms Timeout in this mode.

"ZERO CROSSING DETECTION
The PGA2310 includes a zero crossing detection function
that can provide for noise-free level transitions. The
concept is to change gain settings on a zero crossing of the
input signal, thus minimizing audible glitches.

NB - minimising not eliminating.

This function is enabled or disabled using the ZCEN input
(pin 1). When ZCEN is low, zero crossing detection is
disabled. When ZCEN is high, zero crossing detection will
be enabled.
The zero crossing detection takes effect with a change in
gain setting for a corresponding channel. The new gain
setting will not be latched until either two zero crossings
are detected, or a timeout period of 16ms has elapsed
without detecting two zero crossings. ****In the case of a
timeout, the new gain setting takes effect with no attempt
to minimize audible artifacts.****"

> So if the slider moved a lot in those 50 milli seconds, then you would have to move
> a bit more at once, but during the zero crossing.
> This does actually prevent higher harmonics switching noise.
> I patent this solution hereby, and just because you insulted me and other people
> in your previous rabbit posting, you own me 1000 Internet Credits for every
> device you sell that uses my solution.
>
> I am a bit surprised though that an audiophool genius like you cannot fix a simple
> issue like that all by himself.

A step volume change even at zero cross still results in an instantaneous change in dV/dt which
is still audible and therefore does not solve the basic problem. Also it's not a fade. Fades are
required.


Graham

Phil Allison

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Oct 25, 2008, 11:45:01 AM10/25/08
to
"Eeysore Red Hot Fuckwit "

>>
>> ** Never heard timing the steps to coincide with zero crossings of the
>> signal ???
>
> Yes.
>
>
>> Standard practice is all but low end AV gear.
>>
>> Read the data sheet - dickhead.
>
> And what happens when it times out eh ?


** Nothing worth any worry.

You asinine, ASD fucked pile of fucking pommy puke.


...... Phil


Jan Panteltje

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Oct 25, 2008, 11:55:42 AM10/25/08
to
On a sunny day (Sat, 25 Oct 2008 16:27:18 +0100) it happened Eeyore
<rabbitsfriend...@hotmail.com> wrote in
<49033AD6...@hotmail.com>:

It actually does solve the problem, and anyways 20Hz = 50ms period time, is a zero every 25 mS.
Especially for a fade that happens slowly that should pose no problems.
You could do some math and get slider speed and extrapolate / interpolate a bit too.

If you look for 'eliminating' well, as I have stated, I am no audiophool, and
think that most people will be more then satisfied with the zero crossing solution.

Looked up the PGA2310 datasheet, not bad.
Maybe you have to design your own circuit to work around those 16 ms.
Next time also specify what chip you are using before you ask, and try
reading its datasheet.


Rich Grise

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Oct 25, 2008, 12:01:28 PM10/25/08
to
On Sat, 25 Oct 2008 00:46:44 +0100, Eeyore wrote:

> If so there's a quick question I'd like to run by you.
>

Well I don't know of you've ever herd of the AY3-something or other
sound generator; it had a tone generator and a 4-bit digital attenuator.
You could program it to make a "beep" sound; that was trivially easy.
But once I wrote a little driver that would simulate a "ding" by doing the
"beep" and stepping the attenuator on that standard e^-t time constant
thing; but with only 16 steps, it sounded a little raggedy. That could
be "zipper noise", depending on what's caught in your zipper! ;-D

Is that what you're talking about?

Cheers!
Rich


Martin Griffith

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Oct 25, 2008, 12:10:25 PM10/25/08
to

I've got a complete 6 channel eurocard PCB design using PGA2310's
somewhere, (I never finished the software though).
There was a wolfson chip now obselete, which looked stunning compared
to the TI/BB offering wm 8816? I think someone bought the design from
wolfson

back to my DAC version, (it was for a analogue eq with recall) I think
I had some sucess by putting a little sample and hold that was
switched in during the transition that reduced the glitches by about
30dB, basically a LPF.

Arn't the THAT VCA's good enough?

martin

Eeyore

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Oct 25, 2008, 1:17:31 PM10/25/08
to

"lang...@fonz.dk" wrote:

> Eeyore wrote:
>
> > If so there's a quick question I'd like to run by you.
>

> I have read an article about "gating" the update of level with zero
> crossings to eliminate it.

Put some bass through it and consider how many zero crossings (and how
much time) it'll take to ramp the level down inaudibly. Delay is
unacceptable.

I can only see a viable option being running quickly through all 256 0.5
dB steps. But I'm convinced this will 'zipper'.

Graham

Eeyore

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Oct 25, 2008, 1:22:42 PM10/25/08
to

Jan Panteltje wrote:

> Eeyore wrote in

And the chip wants to see TWO zero crossings. But it times out after 16ms.


> Especially for a fade that happens slowly that should pose no problems.
> You could do some math and get slider speed and extrapolate / interpolate a bit too.
>
> If you look for 'eliminating' well, as I have stated, I am no audiophool, and
> think that most people will be more then satisfied with the zero crossing solution.
>
> Looked up the PGA2310 datasheet, not bad.
> Maybe you have to design your own circuit to work around those 16 ms.
> Next time also specify what chip you are using before you ask, and try
> reading its datasheet.

It was someone else's idea and I'm the one saying "hang on a sec, this isn't going to be adequate".
About a few minutes into reading the datasheet in fact. The originator of the idea is somewhat younger
and less experienced you see. Different approach required IMHO.

Fortunately TI do an (inexpensive - well $99) EV Board - so we can actually put 20Hz through it and
see what happens.

Graham

Eeyore

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Oct 25, 2008, 1:24:23 PM10/25/08
to

Rich Grise wrote:

That's the kind of thing. It's caused by a succession of step changes in
amplitude.

Graham

Eeyore

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Oct 25, 2008, 2:14:59 PM10/25/08
to

Phil Allison wrote:

> "Eeysore Red Hot Fuckwit "
> >>
> >> ** Never heard timing the steps to coincide with zero crossings of the
> >> signal ???
> >
> > Yes.
> >
> >> Standard practice is all but low end AV gear.
> >>
> >> Read the data sheet - dickhead.

See page 10


> > And what happens when it times out eh ?
>
> ** Nothing worth any worry.

Oh really ? I love it when you make a fool of yourself.

" In the case of a timeout, the new gain setting takes effect with no attempt

to minimize audible artifacts."

Not a lot of good for mastering eh ?

Graham


Eeyore

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Oct 25, 2008, 2:32:23 PM10/25/08
to

Martin Griffith wrote:

> I've got a complete 6 channel eurocard PCB design using PGA2310's
> somewhere, (I never finished the software though).
> There was a wolfson chip now obselete, which looked stunning compared
> to the TI/BB offering wm 8816? I think someone bought the design from
> wolfson
>
> back to my DAC version, (it was for a analogue eq with recall) I think
> I had some sucess by putting a little sample and hold that was
> switched in during the transition that reduced the glitches by about
> 30dB, basically a LPF.
>
> Arn't the THAT VCA's good enough?

That's already an alternative suggestion I've made. Thanks Martin. Believe it or not all
this was to try and get 'low cost' matched level controls. Yes, they can do that but
it's for mixing and lag or zipper noise is not acceptable. The originator of the idea
hadn't fully thought it through it seems. And don't forget the predominance of bass in
much music makes the zero-crossing method useless on account of the timeout.

Graham

Jan Panteltje

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Oct 25, 2008, 2:37:55 PM10/25/08
to
On a sunny day (Sat, 25 Oct 2008 18:22:42 +0100) it happened Eeyore
<rabbitsfriend...@hotmail.com> wrote in
<490355E2...@hotmail.com>:

>Fortunately TI do an (inexpensive - well $99) EV Board - so we can actually put 20Hz through it and
>see what happens.

Well, let us know.
But things below 20Hz may be present all by themselves too.
It does not have a brick wall filter at 20 I think, so 10Hz, at less amplitude could
happen too.

In the long ago past (1983 or so) I used some of those 8 bit National DACs with signal on the reference input,
as attenuator, making a zero crossing detector is simple too, some opamps.
But 120dB is difficult.

Have fun.
Better do it all in software?

Eeyore

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Oct 25, 2008, 2:42:37 PM10/25/08
to

Guy Macon wrote:

> Eeyore wrote:
>
> >Anyone here familiar with so-called 'zipper noise' in audio
> >remote/automation level control applications ?
>
> I am very familiar with it. The usual quick and dirty fixes are:
>
> [1] Use lots of bits / high resolution.

Would do if I had them. Only 8 bits of control on the TI PGA2310.


> [2] Slew-rate limit the fader so that is someone slams
> the pot from bottom to top it doesn't skip too many steps.
> This decreases zipper noise at the cost of increasing lag.

Unacceptable for mixing.


> [3] If it's a gain applied to a analog signal, Do the


> actual gain switching at zero crossing. )Note: may conflict
> with [2])

It does conflict, especially at low frequencies. And it still causes an
audible change in dV/dt.


> [3] If the entire signal chain is digital, de-zipper the
> gain change by interpolating a bunch of small steps in software
> between the larger steps from the fader hardware.

Yes, would do but it isn't. It's an analogue signal chain in fact.


> [4] Watch the gain structure so the system isn't using
> the bottom 1% of the fader and following it with high gain
> elsewhere.

Definitely not !

From the other replies you'll probably get the gist of the problem.

In the early days of automated consoles especially, IIRC, 256 discrete
steps would cause zipper noise. Filtering the VCA control input could
make it acceptable but a PGA2310 isn't that kind of chip. Not sure what
control law was being used but if you still only have 256 steps, surely
the same problem exists regardless of the law, it simply moves the
problem around ?

So, digital fails to deliver. I could do it in 24 bit DSP but it would be
plain silly for a volume control. 48kHz sampling would most certainly NOT
be acceptable either so the low cost chips would be out.

Graham

Martin Griffith

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Oct 25, 2008, 2:54:44 PM10/25/08
to

Thats why I junked my 2310 project, potential zipper noise on the
proto, and it was just for the 5.1 monitoring chain, it had some
really neat features, maybe I should look at the files, junk the 8051
for a mega666, put VCA's in......nah, no more dead idea creep

The That2162 is cheap, and dual, that will probably track a bit
better, 'spose you will have to brush up on your tempco compensation
:)

martin

Rich Grise

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Oct 25, 2008, 3:03:30 PM10/25/08
to
So, what was the quesion, or have you already got sufficient answers?

Thanks,
Rich


Eeyore

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Oct 25, 2008, 3:13:45 PM10/25/08
to

Rich Grise wrote:

The answers so far, do peruse them, do indeed confirm my suspicions. I just
wanted to make sure I wasn't going mad etc.

The part in question is being inappropriately promoted for certain uses and a
youngster got caught out by it.

Thankfully we have a Plan B and C !

Graham

Eeyore

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Oct 25, 2008, 3:28:17 PM10/25/08
to

Jan Panteltje wrote:

> On a sunny day it happened Eeyore wrote


>
> >Fortunately TI do an (inexpensive - well $99) EV Board - so we can actually put 20Hz through it >and see what
> happens.
>
> Well, let us know.
> But things below 20Hz may be present all by themselves too.
> It does not have a brick wall filter at 20 I think, so 10Hz, at less amplitude could
> happen too.
>
> In the long ago past (1983 or so) I used some of those 8 bit National DACs with signal on the reference input,
> as attenuator, making a zero crossing detector is simple too, some opamps.
> But 120dB is difficult.
>
> Have fun.
> Better do it all in software?

Well one could but it would be total overkill for this simple requirement.

I think the young lad got a bit carried away with the technology. Always think BASICs first. He seems quite smart
otherwise but I do still feel a little uncomfortable with anyone who codes PICS in a mix of C and assembler. At
least he seems to understasnd what a finite state machine is. I've yet to discover if he knows an interrupt from
polling though (I got a real shock the first time I met a respected programmer who didn't and wondered why his
code would hang !).

Graham


a7yvm1...@netzero.com

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Oct 25, 2008, 5:03:39 PM10/25/08
to
On Oct 25, 12:39 am, Eeyore <rabbitsfriendsandrelati...@hotmail.com>
wrote:

> Paul Probert wrote:
> > Eeyore wrote:
> > > If so there's a quick question I'd like to run by you.
>
> > Are you talking about "motorboating", which you get by biasing a single
> > sided opamp audio circuit by just resistively dividing the power rail?
> > When I turn on a circuit I built that way it does sound like a zipper,
> > ie a run of pulses chirping upward in frequency.

>
> You're referring to power rail modulation classicly caused by insuffient
> local supply decoupling I take it ?
>
> Zipper noise is another effect, essentially a fast series of 'Fourier
> clicks' typically caused by a moderately rapid sequence of step gain
> changes in audio level in a 'fade-out' for example, so called because it
> sounds like the zip on your jeans or whatever. When using a VCA gain
> element it can be 'smoothed' somewhat by RC filtering of the control
> voltage but is inherent in DSP and can only be removed there by making the
> step size very small and therefore all but inaudible.
>
> Graham

Ask Jon Slaughter to design a tube with a level attenuation grid in
it.

Guy Macon

unread,
Oct 25, 2008, 6:55:28 PM10/25/08
to


Eeyore wrote:


>
>Guy Macon <http://www.GuyMacon.com/> wrote:
>
>> Eeyore wrote:
>>
>> >Anyone here familiar with so-called 'zipper noise' in audio
>> >remote/automation level control applications ?
>>
>> I am very familiar with it. The usual quick and dirty fixes are:
>>
>> [1] Use lots of bits / high resolution.
>
>Would do if I had them. Only 8 bits of control on the TI PGA2310.
>
>> [2] Slew-rate limit the fader so that is someone slams
>> the pot from bottom to top it doesn't skip too many steps.
>> This decreases zipper noise at the cost of increasing lag.
>
>Unacceptable for mixing.

Not in all cases. In a case like yours, the lag would almost
certainly be too high, but in a case where the steps are smaller
and the sample rate higher, slew-rate limiting so that the steps
are always monotonic will reduce the residual zipper noise without
any perceptable lag.

>> [3] If it's a gain applied to a analog signal, Do the
>> actual gain switching at zero crossing. )Note: may conflict
>> with [2])
>
>It does conflict, especially at low frequencies. And it still causes an
>audible change in dV/dt.

I did mention that I was listing "the usual quick and dirty fixes"...

Doing the gain switching at zero crossing doesn't totally eliminate
all audio artifacts, but it helps -- a *lot*. A step gain change
at peak amplitude puts a step in the output with the usual deries
of harmonics. A step gain change at zero crossing causes a slope
change with lower harmonic content and less audability.

Anbd, unless one is recording pipe organs or the bass guitar track
on a multichannel recorder, there are almost always enough zero
crossings to avoid triggering any timeout.

>> [3] If the entire signal chain is digital, de-zipper the
>> gain change by interpolating a bunch of small steps in software
>> between the larger steps from the fader hardware.
>
>Yes, would do but it isn't. It's an analogue signal chain in fact.
>
>> [4] Watch the gain structure so the system isn't using
>> the bottom 1% of the fader and following it with high gain
>> elsewhere.
>
>Definitely not !
>
>From the other replies you'll probably get the gist of the problem.
>
>In the early days of automated consoles especially, IIRC, 256 discrete
>steps would cause zipper noise. Filtering the VCA control input could
>make it acceptable but a PGA2310 isn't that kind of chip. Not sure what
>control law was being used but if you still only have 256 steps, surely
>the same problem exists regardless of the law, it simply moves the
>problem around ?
>
>So, digital fails to deliver. I could do it in 24 bit DSP but it would be
>plain silly for a volume control. 48kHz sampling would most certainly NOT
>be acceptable either so the low cost chips would be out.

It looks like you either need to apply the usual quick fixes I listed
that apply and live with the result, or to spend more to buy better
hardware. I know which Mattel would choose... :)


--
Guy Macon
<http://www.GuyMacon.com/>

Guy Macon

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Oct 25, 2008, 6:57:53 PM10/25/08
to


a7yvm1...@netzero.com wrote:

>Ask Jon Slaughter to design a tube with a level attenuation grid in it.

Why, when one could use a servomotor to turn a potentiometer? :)

Phil Allison

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Oct 25, 2008, 8:22:03 PM10/25/08
to
"Eeysore Red Hot Fuckwit "

>
>> > And what happens when it times out eh ?
>>
>> ** Nothing worth any worry.
>
> Oh really ? I love it when you make a fool of yourself.
>
> " In the case of a timeout, the new gain setting takes effect with no
> attempt
>
> to minimize audible artifacts."
>
> Not a lot of good for mastering eh ?


** Yawnnnnnnnnnnnnnnnnnn...

Keep on making wild guesses and wanking off in public.

You FUCKING MORON !!!

..... Phil


Phil Allison

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Oct 25, 2008, 8:24:12 PM10/25/08
to

"Eeysore"

>
> That's already an alternative suggestion I've made. Thanks Martin. Believe
> it or not all
> this was to try and get 'low cost' matched level controls. Yes, they can
> do that but
> it's for mixing and lag or zipper noise is not acceptable. The originator
> of the idea
> hadn't fully thought it through it seems. And don't forget the
> predominance of bass in
> much music makes the zero-crossing method useless on account of the
> timeout.


** More wild guessing and BULLSHIT !!


.... Phil

Rich Grise

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Oct 27, 2008, 12:58:09 PM10/27/08
to
On Sat, 25 Oct 2008 20:13:45 +0100, Eeyore wrote:
> Rich Grise wrote:
>>
>> So, what was the quesion, or have you already got sufficient answers?
>
> The answers so far, do peruse them, do indeed confirm my suspicions. I
> just wanted to make sure I wasn't going mad etc.

Oh, heavens! Everyone's known for some time that you're quite mad, as
am I. ;-)

Cheers!
Rich

Rich Grise

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Oct 27, 2008, 1:00:46 PM10/27/08
to
On Sat, 25 Oct 2008 22:57:53 +0000, Guy Macon wrote:
> a7yvm1...@netzero.com wrote:
>
>>Ask Jon Slaughter to design a tube with a level attenuation grid in it.
>
> Why, when one could use a servomotor to turn a potentiometer? :)

I was going to suggest an analog VCA and a filter on the output of the
DAC. :-)

Cheers!
Rich

in...@rayed.de

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Oct 27, 2008, 4:04:32 PM10/27/08
to
On 25 Okt., 00:46, Eeyore <rabbitsfriendsandrelati...@hotmail.com>

wrote:
> If so there's a quick question I'd like to run by you.
>
> Graham

I have a suggestion:

Decrease the PGA's stepsize by applying dithering to it's 8Bit
control.
As it's update rate could be 390 KHz you have lots of room to increase
the resolution.

A steps increase of 4 Bit would mean the lowest frequency of the
dithering signal is 390KHz/2^4.
This would roughly make the PGA a equivalent linear Multiplier with 8
Bits (instead of 4), so the 8 Bit Quantization noise -48Db (-24Db) is
roughly the maximum zipper noise level.
You can optimize this dithering so that it's amplitude is highest with
highest frequency (bit-reversed counter) and even use more dithering.
Mixing products below 20KHz are then low in amplitude and more
dithering bits still may give audible improvement.

With this gained resolution and high enough update-rate of the
undithered volume control signal you may completely get rid of audible
zipper noises at the expense of mixing products above the audible
range, easily filtered out to some extent and with tolerable residual.

And mind that the dithering gives linear gain change, but the PGA is
exponential.

Martin Griffith

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Oct 27, 2008, 5:39:39 PM10/27/08
to

OK , low cost product.............

martin

Eeyore

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Oct 27, 2008, 8:21:23 PM10/27/08
to

in...@rayed.de wrote:

> Eeyore <rabbitsfriendsandrelati...@hotmail.com> wrote
>
> > If so there's a quick question I'd like to run by you.
>

> I have a suggestion:
>
> Decrease the PGA's stepsize by applying dithering to it's 8Bit
> control.
> As it's update rate could be 390 KHz you have lots of room to increase
> the resolution.

Funny, I had that very same idea only either yesterday or early this
morning.


> A steps increase of 4 Bit would mean the lowest frequency of the
> dithering signal is 390KHz/2^4.
> This would roughly make the PGA a equivalent linear Multiplier with 8
> Bits (instead of 4), so the 8 Bit Quantization noise -48Db (-24Db) is
> roughly the maximum zipper noise level.

That's still a bit high. Noise shaping might help.


> You can optimize this dithering so that it's amplitude is highest with
> highest frequency (bit-reversed counter) and even use more dithering.
> Mixing products below 20KHz are then low in amplitude and more
> dithering bits still may give audible improvement.
>
> With this gained resolution and high enough update-rate of the
> undithered volume control signal you may completely get rid of audible
> zipper noises at the expense of mixing products above the audible
> range, easily filtered out to some extent and with tolerable residual.
>
> And mind that the dithering gives linear gain change, but the PGA is
> exponential.

Yes, another curiosity requiring some form of 'mapping' from one to the
other.

Thanks for your thoughts btw !

As well as the laternative Plan B and C, I have now evolved a Plan D. All
of which will will be much simpler and appeal better to the audio purist.
Looks like the youngster PGA promoter may have to settle for more
conventional level control.

Graham


Eeyore

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Oct 27, 2008, 8:22:42 PM10/27/08
to

Martin Griffith wrote:

> in sci.electronics.design in...@rayed.de wrote:
> >
> >And mind that the dithering gives linear gain change, but the PGA is
> >exponential.
>
> OK , low cost product.............

This is anything but that. When the product literature goes live I can give
a link.

Graham

Jasen Betts

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Oct 29, 2008, 6:56:09 AM10/29/08
to
On 2008-10-25, Eeyore <rabbitsfriend...@hotmail.com> wrote:
>
> Put some bass through it and consider how many zero crossings (and how
> much time) it'll take to ramp the level down inaudibly. Delay is
> unacceptable.
>
> I can only see a viable option being running quickly through all 256 0.5
> dB steps. But I'm convinced this will 'zipper'.

you've proven that 256 steps are insifficient for mastering when the
control will be manipulated during recording.

You need more steps, maybe you can dither the control signal and filter he
dithering out. should be be good for 4 more bits, enough?


--

Bye.
Jasen

JosephKK

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Oct 31, 2008, 12:52:08 AM10/31/08
to
On Sat, 25 Oct 2008 06:39:38 +0100, Eeyore
<rabbitsfriend...@hotmail.com> wrote:

>
>
>Paul Probert wrote:


>
>> Eeyore wrote:
>> > If so there's a quick question I'd like to run by you.
>> >

>> Are you talking about "motorboating", which you get by biasing a single
>> sided opamp audio circuit by just resistively dividing the power rail?
>> When I turn on a circuit I built that way it does sound like a zipper,
>> ie a run of pulses chirping upward in frequency.
>
>You're referring to power rail modulation classicly caused by insuffient
>local supply decoupling I take it ?
>
>Zipper noise is another effect, essentially a fast series of 'Fourier
>clicks' typically caused by a moderately rapid sequence of step gain
>changes in audio level in a 'fade-out' for example, so called because it
>sounds like the zip on your jeans or whatever. When using a VCA gain
>element it can be 'smoothed' somewhat by RC filtering of the control
>voltage but is inherent in DSP and can only be removed there by making the
>step size very small and therefore all but inaudible.
>
>Graham

Nice description. It is pretty rare though, in my experience. I have
heard it only once, and yes it is very obnoxious even at low levels.
It just sticks out, far worse that an abruptly sore thumb.

JosephKK

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Oct 31, 2008, 1:36:00 AM10/31/08
to
On Sat, 25 Oct 2008 11:55:18 GMT, Jan Panteltje
<pNaonSt...@yahoo.com> wrote:

>On a sunny day (Sat, 25 Oct 2008 06:39:38 +0100) it happened Eeyore
><rabbitsfriend...@hotmail.com> wrote in
><4902B11A...@hotmail.com>:


>
>>You're referring to power rail modulation classicly caused by insuffient
>>local supply decoupling I take it ?
>>
>>Zipper noise is another effect, essentially a fast series of 'Fourier
>>clicks' typically caused by a moderately rapid sequence of step gain
>>changes in audio level in a 'fade-out' for example, so called because it
>>sounds like the zip on your jeans or whatever. When using a VCA gain
>>element it can be 'smoothed' somewhat by RC filtering of the control
>>voltage but is inherent in DSP and can only be removed there by making the
>>step size very small and therefore all but inaudible.
>>
>>Graham
>

>Hello Mr Rabbit
>
>That what you call 'zipper noise', is familiar to me.
>You find it for example in my sound blaster (EMU10) based sound card, when moving the slider.
>Now a few interesting points:
>This sound card also does zipper noise when silence, so you hear indeed
>a zipper like noise when the slider moves.
>So the design of the attenuator sucks (Hello Creative Labs).


>
>So, first you should make sure changing attenuator steps (in hardware or software)
>does not cause a signal by itself.
>
>Second, and this is something I have only tested in a *light* related application,
>perhaps you should, or could, switch amplitude only on the zero crossings of the audio
>signal.
>This would mean worst case for 20 Hz every 50 milli seconds,

>So if the slider moved a lot in those 50 milli seconds, then you would have to move
>a bit more at once, but during the zero crossing.
>This does actually prevent higher harmonics switching noise.
>I patent this solution hereby, and just because you insulted me and other people
>in your previous rabbit posting, you own me 1000 Internet Credits for every
>device you sell that uses my solution.
>
>I am a bit surprised though that an audiophool genius like you cannot fix a simple
>issue like that all by himself.
>

>Greetings from
> Dark Fader
>

Well, shucks, Jan. You do some programming in highly interactive but
non real time OS's with high latency GUI. Surely you of all people
can understand that part of the problem is created by how the software
is interacting with hardware. Part of the repeatable issue you have
found is created by this interface. The GUI and the underlying OS for
both most linux distributions and MS OSs are not real time. So the
software accumulates many small steps and sends a 15 to 40 step quanta
to the volume control hardware repeatedly as the visual slider is
moved. The excessive concentration on the visual smoothness results
in zipper noise on the audio path because of the clumping of the audio
control update rate. Correcting the analog attenuator equivalent
portion if the EMU10 design can correct this. It may even be possible
to just issue a software update to do the step interpolation.

JosephKK

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Oct 31, 2008, 1:47:23 AM10/31/08
to
On Sat, 25 Oct 2008 16:27:18 +0100, Eeyore
<rabbitsfriend...@hotmail.com> wrote:

>Exactly the problem. 50ms is too slow. And the chip has a 16ms Timeout in this mode.
>
>"ZERO CROSSING DETECTION
>The PGA2310 includes a zero crossing detection function
>that can provide for noise-free level transitions. The
>concept is to change gain settings on a zero crossing of the
>input signal, thus minimizing audible glitches.
>
>NB - minimising not eliminating.
>
>This function is enabled or disabled using the ZCEN input
>(pin 1). When ZCEN is low, zero crossing detection is
>disabled. When ZCEN is high, zero crossing detection will
>be enabled.
>The zero crossing detection takes effect with a change in
>gain setting for a corresponding channel. The new gain
>setting will not be latched until either two zero crossings
>are detected, or a timeout period of 16ms has elapsed

>without detecting two zero crossings. ****In the case of a


>timeout, the new gain setting takes effect with no attempt

>to minimize audible artifacts.****"


>
>
>> So if the slider moved a lot in those 50 milli seconds, then you would have to move
>> a bit more at once, but during the zero crossing.
>> This does actually prevent higher harmonics switching noise.
>> I patent this solution hereby, and just because you insulted me and other people
>> in your previous rabbit posting, you own me 1000 Internet Credits for every
>> device you sell that uses my solution.
>>
>> I am a bit surprised though that an audiophool genius like you cannot fix a simple
>> issue like that all by himself.
>

>A step volume change even at zero cross still results in an instantaneous change in dV/dt which
>is still audible and therefore does not solve the basic problem. Also it's not a fade. Fades are
>required.
>
>

>Graham

Some of that is the result of when the transitions between the analog
and the digital portions are made and how they are made. I have
already discussed some of the GUI / OS related issues. Converters
have usually carefully managed charge injection issues, not all analog
switches do. Some times the analog switches used in IC converters and
attenuators are not controlled for this property which can contribute
to zipper noise.

Guy Macon

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Oct 31, 2008, 5:12:24 AM10/31/08