Time-stretching best-practices? (for a large file)

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alexdingley
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Time-stretching best-practices? (for a large file)

Post by alexdingley » Sat Nov 16, 2019 1:54 pm

Hi there!

Trying to create an effect... I'm taking a long string of dialog (about 12min) and I'd like to gradually time-compress it to fit into a much smaller time-frame (not sure how long, precisely, that I'd like the end result to be) but I'm going for a sort of gradual time-warp... the first sentence is at regular speed... second sentence gets faster... each few seconds after that, it would start to more notably speed up until it's basically unintelligible. But I'm not sure of any apps / tools that would make this a more expeditious process.

Right now... my workflow is:
1. Select all but the first sentence or so
2. Time-compress it to be about ~75% of the original length
3. Select from a little farther along in the (now already partially compressed audio)
4. Time-compress it to be about ~75% of the current length.
repeat steps 3 & 4 until I've gotten to the end....

but even with a 12-Core Mac Pro & 64GB of RAM... this is a slow workflow. I can imagine having to do 15-20 passes and (sure they'll get shorter as I go, but) it's pretty laborious in the above method.

In my head, I'm imagining a solution & wishing there was some kind of tool that could allow me to draw an automation line that expresses "rate of speed-change", so that I could draw a nice logarithmic arc and see if it sounded nice... then change the taper to suit my tastes. That's probably not something that's out there — but if any of you know any really snazzy time-compression tools, I'd be really curious to check one out.

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Re: Time-stretching best-practices? (for a large file)

Post by kslight » Sat Nov 16, 2019 4:18 pm

I don’t know what daw you’re using nor have I tried it but if you have “elastic audio” or the equivalent turned on and then made constant tempo automation that it could follow I think that work work?

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Re: Time-stretching best-practices? (for a large file)

Post by digitaldrummer » Sun Nov 17, 2019 9:03 am


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Re: Time-stretching best-practices? (for a large file)

Post by drumsound » Mon Nov 18, 2019 8:20 am

digitaldrummer wrote:
Sun Nov 17, 2019 9:03 am
so you can do this?

https://www.youtube.com/watch?v=LVbdzieh32E

:shock:
Making the studio version sound like they sounded live back then...

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Re: Time-stretching best-practices? (for a large file)

Post by The Scum » Mon Nov 18, 2019 9:58 am

I think the progressive approach you're describing might involve more sonic degradation that some other approaches. The tail of the program will have been resampled many times. A better approach might be to select the "next" sentence, scale it up, then select the next after that, and scale it up by a little bit more.libsamplerate. Of course, if the intended target is unintelligible, then it might not be such a big concern.

How good are your programming chops?

libsamplerate can do ramping between subsequent calls. From their docs:
When using the src_process or src_callback_process APIs and updating the src_ratio field of the SRC_STATE struct, the library will try to smoothly transition between the conversion ratio of the last call and the conversion ratio of the current call.
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Re: Time-stretching best-practices? (for a large file)

Post by markjazzbassist » Mon Nov 18, 2019 10:21 am

buy a cassette deck or reel to reel with 2 speeds and variable pitch. start on slow speed with pitch all the way down, record to this. on playback increase speed then hit hi speed switch and jack up the speed there too.

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Re: Time-stretching best-practices? (for a large file)

Post by Magnetic Services » Mon Nov 18, 2019 12:22 pm

Stretch Markers in Reaper are your best friend:

https://www.youtube.com/watch?v=rid4NpN8mqY

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Re: Time-stretching best-practices? (for a large file)

Post by alexdingley » Tue Nov 19, 2019 9:05 am

ha! good ideas all around. I ended up doing a mix of methods to get it to sound the way I wanted... But Stretch Markers is a SUPER smart move, and I'm surprised it didn't occur to me prior. I'm in Logic Pro X, and I do plenty of flex-time work, so I should have just tried that from the start...

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