[RWP] Time alignment of audio from multiple sources

[Scott Chesworth]

hahaha, yeah, that does seem to be the order of the day. Ah well, it's
a learning experience I guess. Thanks Zoom.

On 12/18/14, Patrick Perdue <patrick at pdaudio.net> wrote:
> I've done this multi-device recording gig before. Even if you carefully plot
> out a constant sampling rate offset, it still won't quite work out. Some of
> these things don't even drift at the same rate from other sources.
> Potentially lots of manual nudging from time to time is in your future, even
> if you get things lined up for a while.
>
>> On Dec 17, 2014, at 8:19 PM, Jim Snowbarger <snowman at SnowmanRadio.com>
>> wrote:
>>
>> I would guess that, even though they will be quoted as being identical,
>> the
>> frame rates actually are different.  The fact is that they were recorded
>> with devices each of which had it's own time base crystal, and thus it's
>> own
>> idea of the actual length of a microsecond.  One always has this problem
>> in
>> sinking recordings that were made on separate devices.  They don't have a
>> common time base.
>> You might be able to eventually tame that down by taking one of them into
>> sound forge and changing the sample rate, setting the sample rate only.
>> The hard part is how much to change the sampel rate, and in what
>> direction,
>> in order to get compliance.  The way I do it is to position them so they
>> start in sink, and then go to the end, are try to judge how much time lag
>> has developed, over how long an interval.
>> That workks ok for long clips, but not so well for short ones.
>> But then, it is the long one's that give you enough time for the mismatch
>> to
>> become apparent.
>> Once a significant mismatch has developed, you can often learn to judge
>> the
>> number of milliseconds involved just by the sound of the composite mix.
>> Make one signal louder thant the other.  So, you can tell just by
>> listening,
>> whether the lould signal comes first, or the soft one.  The later is a
>> bit
>> like reverse reverb effect.  So, now you know who is slow and who is
>> fast.
>> Next, is to estimate the number of milliseconds involved.  A handy place
>> to
>> judge that might be where there is a sharp edge, like a wood blick hit,
>> or
>> other sharp percussive,  listen to how the sharp edge is spattered by the
>> two competing signals.  If you guess right, then divide that estimate to
>> the
>> total length of the sample, and that will tell you by what percent the
>> clocks differ.  Change the sample rate by that percentage, setting the
>> sample rate only, and see what happens.  Your results will vary.
>>
>>
>>
>>
>>
>> -----Original Message-----
>> From: RWP [mailto:rwp-bounces at reaaccess.com] On Behalf Of Scott Chesworth
>> Sent: Wednesday, December 17, 2014 6:22 PM
>> To: Reapers Without Peepers
>> Subject: [RWP] Time alignment of audio from multiple sources
>>
>> Hey folks,
>>
>> I'm sat here mixing a multitracked live recording. There are a bunch of
>> close mics and a couple of DI sources that were tracked with a Zoom R16,
>> and
>> the band would like me to use the audio from a Zoom Q3 camera as ambient
>> mics. But here's the thing, I'm having no luck at all getting the audio
>> from
>> the Q3 synced with the audio from the R16, and I've not struggled with
>> this
>> task before, so thought I'd ask whether anyone here had a decent workflow
>> for getting the job done. At the moment I'm just nudging in small
>> increments
>> and listening. I can get the alignment so that it sounds fine on one part
>> of
>> a song, but then skipping forward a minute or so I'm hearing flamming on
>> pronounced drum fills etc. It's almost like the frame rates of the two
>> sources are different or something.
>>
>> Any thoughts or advice?
>>
>> Scott
>>
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