Mic power control

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Alex

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Jun 6, 2011, 4:51:32 AM6/6/11
to Magic Lantern firmware development
After a comment regarding input impedance for microphone, I took a
quick look in the AK4646 datasheet and noticed this [p.31]:

"The AK4646 has a gain amplifier for microphone input. The gain of
MIC-Amp is selected by the MGAIN2-0 bits (Table 19). The typical input
impedance is 30kΩ (typ)."

In audio.c, ML enables microphone power by default, and in this case:

"When PMMP bit = “1”, the MPWR pin supplies power for the microphone.
This output voltage is typically 0.8 x AVDD and the load resistance is
minimum 0.5kΩ. In case of using two sets of stereo microphone, the
load resistance is minimum 2kΩ for each channel. "

There are quite a bit of issues saying certain microphones have low
input levels with Magic Lantern (e.g. Rode VideoMic). It may be
possible that the cause may be the lower input impedance caused by
forcing mic-power on, even if it's not needed.

Therefore, I've created an experimental changeset which adds mic power
control to the user interface, to see if it helps fixing low input
level issues:

https://bitbucket.org/hudson/magic-lantern/changeset/7e54c91ac878 550D
https://bitbucket.org/hudson/magic-lantern/changeset/c6497b2166dc 60D

I did not run this code yet, because I have no camera with me right
now (I'll test tonight). If you can compile this code and run some
tests, it would be great. If you want to run my untested
autoexec.bin's (for either 550D or 60D), just ask.

Morgan Look

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Jun 6, 2011, 6:10:09 AM6/6/11
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HI Alex.

It certainly looks that disabling the mic power will remove approx 2k of (parallel) impedance from the input.
The internal microphone requires power, so disabling it only makes sense for modes that don't also use the internal mic.
It's also probably a good idea to offer a ext balanced only (no internal) option with power off, since the power configuration is incompatible with balanced mics anyway (see fig 23 as implemented by canon vs fig 22 requirement for balanced mic with power). This would allow powering balanced mics without any further decoupling capacitors.

Morgan.

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Alex

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Jun 6, 2011, 6:15:39 AM6/6/11
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Thanks Morgan,

So, you suggest that, instead of a separate mic-power item in menu, we
should have these options under the input source?

- internal mic (power=1)
- int Left ext Right (power=1)
- external stereo (power=1)
- external stereo high-Z (power=0)
- int Left ext Balanced (power=1)
- Balanced high-Z (power=0)
- Auto int/ext (how to detect if a mic needs power or not?!)

Any suggestions about the wording for these options in the menu?

Morgan Look

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Jun 6, 2011, 6:52:29 AM6/6/11
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Dunno, I think I prefer a separate menu item for mic power, with a note that it gets ignored (grayed out?) in any case where the internal mic is enabled. If there isn't room for another menu item then a list with every option would work too.

Additionally; A balanced mic will always "see" the 2k resistors. With mic power enabled this will present 2k impedance to AC ground on each side (not sure if this is equivalent to 1k in a balanced case or not?). With mic power disabled this will present 4k (2x2k in series) impedance across the balanced lines.
Hmm... also in the stereo case there is 4k between the channels (but not to AC ground), not sure what effect this will have.

Also powering a balanced mic without additional decoupling will mean that the internal mic is connected via a (star) network of 2k resistors, but "should" be getting zero volts (assuming all 2k resistors are of equal value). Either way it's probably safe, I'm just putting it here so people have been warned.

Morgan.

Alex

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Jun 6, 2011, 7:18:32 AM6/6/11
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Right now there is a separate menu item for mic power.

Alex

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Jun 6, 2011, 7:36:13 AM6/6/11
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Just implemented some UI changes for the mic power menu item: it
displays "High Z" and "Low Z" in addition to ON/OFF, and it forces
power on for "internal mic" and "int Left ext Right". If the actual
setting is different than what you have set in menu, the icon will be
a red circle.

https://bitbucket.org/hudson/magic-lantern/changeset/195d5b97fc64

Can you suggest a better help text for this item? (58 characters max).

thba74

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Jun 6, 2011, 8:02:40 AM6/6/11
to Magic Lantern firmware development
Can attach a autoexec.bin for testing?

On 6 Jun., 13:36, Alex <broscutama...@gmail.com> wrote:
> Just implemented some UI changes for the mic power menu item: it
> displays "High Z" and "Low Z" in addition to ON/OFF, and it forces
> power on for "internal mic" and "int Left ext Right". If the actual
> setting is different than what you have set in menu, the icon will be
> a red circle.
>
> https://bitbucket.org/hudson/magic-lantern/changeset/195d5b97fc64
>
> Can you suggest a better help text for this item? (58 characters max).
>
>
>
>
>
>
>
> On Mon, Jun 6, 2011 at 1:18 PM, Alex <broscutama...@gmail.com> wrote:
> > Right now there is a separate menu item for mic power.
>
> > On Mon, Jun 6, 2011 at 12:52 PM, Morgan Look <morgan.l...@gmail.com> wrote:
> >> Dunno, I think I prefer a separate menu item for mic power, with a note that it gets ignored (grayed out?) in any case where the internal mic is enabled.  If there isn't room for another menu item then a list with every option would work too.
>
> >> Additionally; A balanced mic will always "see" the 2k resistors.  With mic power enabled this will present 2k impedance to AC ground on each side (not sure if this is equivalent to 1k in a balanced case or not?).  With mic power disabled this will present 4k (2x2k in series) impedance across the balanced lines.
> >> Hmm... also in the stereo case there is 4k between the channels (but not to AC ground), not sure what effect this will have.
>
> >> Also powering a balanced mic without additional decoupling will mean that the internal mic is connected via a (star) network of 2k resistors, but "should" be getting zero volts (assuming all 2k resistors are of equal value).  Either way it's probably safe, I'm just putting it here so people have been warned.
>
> >> Morgan.
>
> >> On 6/06/2011, at 10:15 PM, Alex wrote:
>
> >>> Thanks Morgan,
>
> >>> So, you suggest that, instead of a separate mic-power item in menu, we
> >>> should have these options under the input source?
>
> >>> - internal mic (power=1)
> >>> - int Left ext Right (power=1)
> >>> - external stereo (power=1)
> >>> - external stereo high-Z (power=0)
> >>> - int Left ext Balanced (power=1)
> >>> - Balanced high-Z (power=0)
> >>> - Auto int/ext (how to detect if a mic needs power or not?!)
>
> >>> Any suggestions about the wording for these options in the menu?
>
> >>>>> For more options, visit this group athttp://groups.google.com/group/ml-devel?hl=en
>
> >>>> --
> >>>>http://magiclantern.wikia.com/
>
> >>>> To post to this group, send email to ml-d...@googlegroups.com
> >>>> To unsubscribe from this group, send email to ml-devel+u...@googlegroups.com
> >>>> For more options, visit this group athttp://groups.google.com/group/ml-devel?hl=en
>
> >>> --
> >>>http://magiclantern.wikia.com/
>
> >>> To post to this group, send email to ml-d...@googlegroups.com
> >>> To unsubscribe from this group, send email to ml-devel+u...@googlegroups.com
> >>> For more options, visit this group athttp://groups.google.com/group/ml-devel?hl=en

Alex

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Jun 6, 2011, 9:45:30 AM6/6/11
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Sure. This one is for 550D/1.0.9. I did not run it on my camera, so
there may be surprises.
autoexec.bin

Alex

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Jun 6, 2011, 9:47:40 AM6/6/11
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And this one is for 60D/1.0.9 (again, not tested). Be careful not to
mix them up.
autoexec.bin

Chris71

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Jun 6, 2011, 1:00:01 PM6/6/11
to Magic Lantern firmware development
I tried the Mic Power setting with my Soundman OKM II microphone
(which needs phantom power to work.)

When the setting is "OFF (High Z)", my external microphone doesn't
work anymore, when the setting is "ON (Low Z)", it's working again. I
tried it both with "Auto INT/ext" and "external stereo".

So from what I could test, the new option seems to work.

I would rather call this option "Phantom Power". Help text could be
"Needed for int. and some other mics, but lowers impedance."

On 6 Jun., 15:47, Alex <broscutama...@gmail.com> wrote:
> And this one is for 60D/1.0.9 (again, not tested). Be careful not to
> mix them up.
>
> On Mon, Jun 6, 2011 at 3:45 PM, Alex <broscutama...@gmail.com> wrote:
> > Sure. This one is for 550D/1.0.9. I did not run it on my camera, so
> > there may be surprises.
>
> > On Mon, Jun 6, 2011 at 2:02 PM, thba74 <svenwut...@web.de> wrote:
> >> Can attach a autoexec.bin for testing?
>
>
>
>  autoexec.bin
> 226KAnzeigenHerunterladen

JaKob

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Jun 6, 2011, 1:06:13 PM6/6/11
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wow for real?!? got a link for the mic ?

- Jakob


Chris71

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Jun 6, 2011, 1:38:58 PM6/6/11
to Magic Lantern firmware development
The mic I'm using is called OKM II K (Classic), an in-ear microphone
that lets you make binaural recordings. I like it because you just
wear it in your ears when recording and there is no need to connect
something to the camera (except the mic cord.)

Some links are:
http://www.soundman.de/englisch/english.htm (manufacturer)
http://emusician.com/mics/emusic_soundman/ (review)
http://www.okm2.de/ (in German, but with references to the
550D, the 60D and even Magic Lantern :-)

On 6 Jun., 19:06, JaKob <jakob...@gmail.com> wrote:
> wow for real?!? got a link for the mic ?
>
> - Jakob
>

thba74

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Jun 6, 2011, 3:15:06 PM6/6/11
to Magic Lantern firmware development
In this relation "phantom power" is not the correct term. +48V phantom
power is needed by condenser microphones like the Sennheiser ME66. The
550D mic jack brings out an so called "Mic Plug-in Power", typically
2-3V DC.

Piers

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Jun 7, 2011, 6:27:02 AM6/7/11
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I second that - phantom power is +48V (a ludicrously high value chosen several eras ago). However, it is power of some sort, not just impedance. 

PG

Alex

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Jun 21, 2011, 8:17:30 AM6/21/11
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Here's a quick and dirty patch for audio.c which does this:

1) displays the digital gain used by AGC, when that setting is on;
2) allows you to change the digital output gain, which might increase
the volume for audio monitoring;
3) uses Morgan Look's masked_audio_ic_write to preserve the values of
some audio flags which seem unrelated to ML (effects of those flags
are unknown to me right now).

This patch should work unchanged on 550D and 60D, and maybe on 5D2 too.

Also, I've noticed that AGC is only applied in digital domain (i.e.
analog gain still has effect even if AGC is on, and this is confirmed
by the datasheet).

I don't have the cables with me right now to test it myself. Does it work?

If you don't know how to use a patch:
1) patch -p1 < audio.patch
2) http://magiclantern.wikia.com/wiki/Build_instructions/550D

audio.patch
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