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Author Topic: SBD/AUD Matrix Pitch Question  (Read 5313 times)

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Offline Life In Rewind

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Re: SBD/AUD Matrix Pitch Question
« Reply #15 on: July 29, 2015, 02:21:43 AM »
My approach has always been to alter the trackset that I planned to use the LEAST in the mix
^^^
That's logical.

I typically shrink the longer file rather than stretch the shorter one-  Just as best practice, since in terms of information that's equivalent to reducing rather than enlarging an image.  Generally, one can't create new information to 'fill the gaps' as transparently and potentially artifact-free as discarding excess information, although it's questionable if it really matters or not since the change isn't usually all that large.

I think the jpg image analogy was once addressed...and isn't as useful in the audio realm as we might like...

I get it - but aren't we just (ideally) changing the speed of one recording relative to another via clock?

Clock 1 is a SBD
Clock 2 is an AUD
Clock 3 is the playback device - and this is where the differences in speed are juxtaposed/announced via drift.(because 1 and 2 are slightly different)

Essentially you have one source that is "out of tune" with the other...its faster by a tiny, tiny amount.

Probably beyond most folks ears (including mine) to hear on individual sources - but obvious when you get a half hour in an the sources are out of sync.

I guess the problem is - we aren't correcting via the 3rd clock - but via resampling one of the sources...(or something, depending on your software)

If I have a solid SBD - and just want to sprinkle a few db of AUD ambience over it...why screw with the SBD?
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Offline Gutbucket

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Re: SBD/AUD Matrix Pitch Question
« Reply #16 on: July 29, 2015, 09:45:58 AM »
Changing runtime while also affecting pitch is easy.  Just adjust the playback rate.  No information is added or lost.  The image analogy holds in that case.
Its changing the run time without affecting pitch which is trickier, but made simple with the advanced tools now available.

I was about to say that the slight pitch change produced by changing the run time of one file to sync with the second is probably not significant enough to matter, and regardless of how it's done I expect that is the case.  But you've got me thing through this again, and I now realize that actually we do want to change pitch as well as timing, and I may have been selecting the incorrect mode in Samplitude's stretch algorithm.  I'll have to check that..  I may have been stretching to sync timing between two files, and unintentionally throwing the pitch off slightly, by instructing the algorithm NOT to allow any change of pitch change with the stretch.  Instead, we want the pitch changed as well, to bring it the two slightly different pitches back into union.  I'll walk through it below, but if this is correct, it ironically proves to me that the typical amount of time stretch required isn't significant enough to cause serious pitch problems, since I didn't notice any that I may have unintentionally introduced!

Scenario:
Two different recorders with unsync'd clocks record the same sound (with a pitch and duration), sampling at a slightly different rate.  Upon playback directly from the same machines on which they were recorded, using the same recording clocks for playback as were used for recording, the sound from both will remain in sync once initially sync'd.  I used to play back this way regularly, having trained myself to hear the slight delay or lack of it once the two were effectively in perfect sync, the more difficult task of properly identifying which was leading and which was lagging, and perfection of a very rapid "play/pause/play" jab.

The same two files, transferred off the original machines on which they were recorded, are then played back with timing provided by a third clock.  The rate of the third differs slightly from both of the recording clocks.  Both play back at a slightly different pitch and duration than the original.  One is adjusted to match the other, and that accurate relative sync between the two is good enough.  Absolute sync to the exact timing and pitch of the original (by adjusting the rate of the third clock) isn't perfectly maintained and isn't critical, only the relative timing of the two.  Playback rate and pitch going to vary ever so slightly with each different playback device based on the difference between it's own clock (the new 3rd) and the clock of the original  recorder (the 1st), the file of which was never changed.
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Offline Gutbucket

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Re: SBD/AUD Matrix Pitch Question
« Reply #17 on: July 29, 2015, 10:01:36 AM »
If I have a solid SBD - and just want to sprinkle a few db of AUD ambience over it...why screw with the SBD?

I agree that your general rule of adjusting whichever source will be providing the lower level in the final mix is a good one.

When you say "If I have a solid SBD - and just want to sprinkle a few db of AUD ambience over it.."  You don't mean you will be using a level of only a few dB for the AUD.  That would be so low in level it would be completely inaudible.  You are actually talking about a few dB over the threshold of audibility, and the level of audibility is primarily determined by the level and content of the other source.  Similar to the timing issues, it is the difference in level between the two which is more key than the absolute level of either one.

If heard at all, the difference in level between the two isn't going to be overly large, otherwise the quieter source would be completely masked by the louder one. Granted, if the relative level of the second is only barely audible under the first, any low level artifacts in the quieter source will probably be completely masked.  Yet I never know beforehand exactly what balance I'm going to end up with between the two sources, so just I shrink the longer one and realize that it probably doesn't make a significant difference either way.


Resampling will lock and adjusted non-standard playback timing/pitch to a new standard nominal playback rate.

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Re: SBD/AUD Matrix Pitch Question
« Reply #18 on: July 29, 2015, 11:58:45 AM »
I now realize that actually we do want to change pitch as well as timing

That's always been my assumption — that different sample rates reflect different pitches as well as tempo, like cassette players running at two different speeds. I always choose to link pitch and tempo when making adjustments for matrixing, for this reason.

(Though to be honest, over the sorts of time scales we're typically working with here, I expect pretty much no one will be able to hear the difference between repitched and non-repitched.)

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Re: SBD/AUD Matrix Pitch Question
« Reply #19 on: July 29, 2015, 12:06:55 PM »
My hand-calculated method (in Sound Studio, but should work in most audio editors), FYI if it's useful to anyone:

1) Mark two points (usually a loud clap or snare hit or other item with a sharp attack that can be easily pinpointed) near the beginning and end of the two sources.

2) Measure the distance between the markers in each source.

3) Convert to seconds.

4) Divide the longer length by the shorter one.

5) Multiply by 100 to get a percentage rather than a decimal.

6) Adjust the tempo of the longer-length source by the percentage in Step 5.

7) Cut and mix paste to taste.

And no, I've never noticed any artifacts from this, nor from stretching files that are too fast, either.

Offline Gene Poole

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Re: SBD/AUD Matrix Pitch Question
« Reply #20 on: July 29, 2015, 11:48:55 PM »
A clock difference is going to affect both the tempo and the pitch.  To account for both, adjust the speed (audacity has a setting for this).  The sample rate change trick works as it only affects the speed.

Offline hoserama

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Re: SBD/AUD Matrix Pitch Question
« Reply #21 on: July 30, 2015, 02:53:12 AM »
My hand-calculated method (in Sound Studio, but should work in most audio editors), FYI if it's useful to anyone:

1) Mark two points (usually a loud clap or snare hit or other item with a sharp attack that can be easily pinpointed) near the beginning and end of the two sources.

2) Measure the distance between the markers in each source.

3) Convert to seconds.

4) Divide the longer length by the shorter one.

5) Multiply by 100 to get a percentage rather than a decimal.

6) Adjust the tempo of the longer-length source by the percentage in Step 5.

7) Cut and mix paste to taste.

And no, I've never noticed any artifacts from this, nor from stretching files that are too fast, either.

I do something similar but much more fine tuned. Even did a youtube video tutorial of it! Requires Adobe Audition and excel.

https://www.youtube.com/watch?v=MOz2GUdL_vw&feature=youtu.be
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Re: SBD/AUD Matrix Pitch Question
« Reply #22 on: August 10, 2015, 09:43:41 PM »
I've long been under the intuitive impression that it's a better idea to throw away data to "Squash" the longer source, rather than forcing my free software to make up data where there was none!?!




You will need to stretch one of the recordings to fit.

DISCLAIMER: Purely anecdotal, non-scientific-in-any-way and nit-picking statement-

I've found that stretching the "shorter" (for lack of a better term) of the 2 recordings can *sometimes* add a few little bits of digi-noise here and there. Maybe 3 to 6 of them over the course of a 2 hour recording and they can be somewhat obvious to very subtle and they probably only bug me because I know they are there... I'm talking sub-1-second little snits.

Conversely and again, purely anecdotal, but IMHO and also IME throwing away a few samples from the "longer" recording by shrinking it doesn't *seem* to introduce these little bits of digi-noise nearly as much.

Hope this makes sense.


WE ABSOLUTELY WANT TO SHIFT PITCH when we are correcting for mismatched clock speeds!  That's the point! Shift pitch in order to make the sources match in length.

Also, watch out for if the mics get moved. If the distance changes between the sources, the correction would change! I noticed this when I've stuck my audio over videos where I go from the back of the room up to the stage, or vice versa. My solution there is to get the synch close enough, within one frame of video, and set it so that despite any drift, the sound never arrives before the picture.

I now realize that actually we do want to change pitch as well as timing

That's always been my assumption — that different sample rates reflect different pitches as well as tempo, like cassette players running at two different speeds. I always choose to link pitch and tempo when making adjustments for matrixing, for this reason.

(Though to be honest, over the sorts of time scales we're typically working with here, I expect pretty much no one will be able to hear the difference between repitched and non-repitched.)
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Offline Gutbucket

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Re: SBD/AUD Matrix Pitch Question
« Reply #23 on: August 11, 2015, 12:04:42 PM »
WE ABSOLUTELY WANT TO SHIFT PITCH when we are correcting for mismatched clock speeds!  That's the point!

Well it's half the point.  Timing is the other half, the far more obvious half.

Quote
Shift pitch in order to make the sources match in length.

No. 

With modern audio tools, pitch and time need not remain linked anymore.  So we can shift pitch without changing length if we want to.  But that's not appropriate for this problem.

That should read "shifting pitch and length together to make the two sources match."  The pitch and time remaining linked.

Quote
Also, watch out for if the mics get moved. If the distance changes between the sources, the correction would change! I noticed this when I've stuck my audio over videos where I go from the back of the room up to the stage, or vice versa. My solution there is to get the synch close enough, within one frame of video, and set it so that despite any drift, the sound never arrives before the picture.

That only requires a time-shift.  Not a length/pitch shift to match to different clock sources, but re-alignment of two identical clocks which are shifted in time.
« Last Edit: August 11, 2015, 12:06:50 PM by Gutbucket »
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Offline morst

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Re: SBD/AUD Matrix Pitch Question
« Reply #24 on: November 04, 2015, 04:05:45 PM »
WE ABSOLUTELY WANT TO SHIFT PITCH when we are correcting for mismatched clock speeds!  That's the point!

Well it's half the point.  Timing is the other half, the far more obvious half.

D'OH!  :facepalm:
Quote
Quote
Shift pitch in order to make the sources match in length.

No. 

With modern audio tools, pitch and time need not remain linked anymore.  So we can shift pitch without changing length if we want to.  But that's not appropriate for this problem.

That should read "shifting pitch and length together to make the two sources match."  The pitch and time remaining linked.


Excellent distinction! I don't use "pitch shifting" effects to do it noticeably, I use the one called "speed change" which does shift pitch and length together. Good call to mention that.
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Offline StarkRavingCalm

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Re: SBD/AUD Matrix Pitch Question
« Reply #25 on: November 04, 2015, 05:56:39 PM »
Try using Reaper, there's feature called Nudge that works great for this very purpose.
All it does it shift the file in the direction you tell it to.
Once you import the files, you right click on the SBD file and choose Nudge\Set.
Works perfectly.

Offline Ben Turnbull

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Re: SBD/AUD Matrix Pitch Question
« Reply #26 on: November 08, 2015, 04:43:59 PM »
How does this Nudge thingie work?  Is it an alignment tool or does it put a marker/hold on a spot and bump everything right of the mark over a bit?
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Re: SBD/AUD Matrix Pitch Question
« Reply #27 on: December 18, 2015, 06:14:11 PM »
I do source matching in Wavelab > audio montage

first I match files at the beginning then I move tot the end and choose 2 points unmatched.
I "split at cursor" the file to be stretched and use the function "Transform > time stretch to cursor"

Offline StarkRavingCalm

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Re: SBD/AUD Matrix Pitch Question
« Reply #28 on: December 18, 2015, 07:33:45 PM »
How does this Nudge thingie work?  Is it an alignment tool or does it put a marker/hold on a spot and bump everything right of the mark over a bit?

Sorry for the delay...
You can move by position or by the edge of the file.
I always use position cause you dont always know exactly where the extra space is

 

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