[QLab] looping gives click at loop point, only in qlab

[Martin .]

Hi list,

should I take any special precautions when looping soundfiles in qlab?
Does it cut off any samples or interpolate? I got a soundfile which
loops nicely in Audacity, SuperCollider and Pro Tools but gives off a
click at the loop point in qlab. I can send the file if necessary.

cheers,

martin
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[Jeremy Lee]

Is your entire file loopable, or are you trying to set a loop in the
middle of the file? The math can get a bit tricky if you're trying to
do the latter. I've never had a problem when I make the entire file
loop properly.

QLab isn't going to make a crossfade loop or anything else for you.
It's up to you to make sure that the last sample loops back to the
first sample without error.

Best,

Jeremy

On Sep 7, 2009, at 10:24 AM, Martin . wrote:

> Hi list,
>
> should I take any special precautions when looping soundfiles in qlab?
> Does it cut off any samples or interpolate? I got a soundfile which
> loops nicely in Audacity, SuperCollider and Pro Tools but gives off a
> click at the loop point in qlab. I can send the file if necessary.
>
> cheers,
>
> martin

--
Jeremy Lee
Sound Designer, NYC - USA 829
http://www.jjlee.com

[Martin .]

Hi,

yes, it's the entire file. I found it quite strange, like I said it
loops perfectly in several other applications (without any
crossfading/interpolation). I have also disabled the 'Guarantee
Synchronization' since it says it shaves off a small bit of audio.

cheers,
martin

[Christopher Ashworth]

Hi Martin,

I have the example file and workspace you provided in this ticket:

http://tracker.figure53.com/qlab/ticket/459

And I'm hoping to spend some time digging in to what might be
happening, but I have not yet had time to explore in detail.

However, I did see that for some reason in the waveform view in QLab
the waveform at the beginning of the file and at the end of the file
do not initially look like they match up. This may several things: it
may be an artifact of the way QLab draws the waveform, and the
accuracy of the drawing is not enough to show that they actually match
up, it may be a bug in reading the samples, or it may be that the
samples are not in fact actually matching. I have not yet pulled
specific numbers out of the file to know for sure.

I cannot speak to what those other programs do with looping files.
It's entirely possible they do some kind of smoothing function; I
wouldn't know. I do know that I've set up many loops in QLab and not
had any clicking. I'll need to investigate this specific file more
closely to figure out what is happening here.

The guarantee sync feature will not affect looping. If frames are
lost with this feature it is only the first time at the top of the
file--not when it loops.

Best,
Chris

[Martin .]

Hi Chris,

Thanks - although it was not me posting the ticket. I'll upload the
file and post at the site so you can check that too.

Note to self: check the bug tickets before posting to list :)

cheers,
martin

[Christopher Ashworth]

Oh, ha! Sorry!

Note to self: Don't go assuming similar reports are from the same
person!

Best,
Chris

On Sep 8, 2009, at 2:55 PM, Martin . wrote:

> Hi Chris,
>
> Thanks - although it was not me posting the ticket. I'll upload the
> file and post at the site so you can check that too.
>
> Note to self: check the bug tickets before posting to list :)
>
> cheers,
> martin

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[Sean Dougall]

I've done a bit of investigation into this, and I've found what looks
like a clue as to what's going on. It seems like it's a function of
the data structure QuickTime uses for measuring time, which rounds its
measurements to the nearest 1/600 of a second (and apparently is only
playing back audio up to the nearest 1/600 second).

Fixing it is another issue, of course, but just an FYI. I've updated
the ticket at http://tracker.figure53.com/qlab/ticket/459.

-Sean

(P.S. Martin, if you could send me a link to your problem file, that
would still be helpful as another test case. Thanks!)

On Sep 8, 2009, at 11:55 AM, Martin . wrote:

> Hi Chris,
>
> Thanks - although it was not me posting the ticket. I'll upload the
> file and post at the site so you can check that too.
>
> Note to self: check the bug tickets before posting to list :)
>
> cheers,
> martin
>
> On Mon, Sep 7, 2009 at 9:57 PM, Christopher Ashworth<ch...@figure53.com
> > wrote:
>> Hi Martin,
>>
>> I have the example file and workspace you provided in this ticket:
>>
>> http://tracker.figure53.com/qlab/ticket/459
>>

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