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Mojo3432
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2014/08/19 10:29:48 (permalink)

Time Stretching Question

Hello My Fellow "Sonar-ians",
 
I have a question about time stretching a piece of audio and want to know if I'm either missing something or if there is any way to make it more accurate.
 
Here is my scenario and please forgive the lengthy explanation:  I am working on a project with a tempo of 119.  In this project there is a guitar arpeggio which needs to be finger-picked.  The problem is that I can't play it cleanly/accurately at 119.  So I reset the tempo to be 40% slower (71.4) so that I can play along and record the part accurately.  Then, I readjust the tempo back to 119 and time stretch (in reverse) the audio clip from 100% down to 60%.  Thus, speeding it up by 40%.
 
This is great in theory, however, I'm finding that it's not completely accurate.  When "squeezing" the audio down to 60% and viewing the % in yellow up in the right hand corner of the clip - I can hit 60% and even continue to squeeze it down a few more notches and it will still read 60% before it will hit 59%.
 
My question is WHY?  There really shouldn't be any extra slack in there.
Shouldn't each increment you squeeze or stretch the audio be a the next % in value?  
60%, 59%, 58%, 57% etc....not 60%, 60%, 60%, 59%, 59%, 59%.....
 
If I play back my arpeggio at the reduced tempo - it is spot on in synch.
I find that to speed it back up, I really have to mess with it quite a bit and tweak it here and there before it will lock to the faster tempo.
 
Am I missing something or is that just the nature of the beast?
 
Thanks for your help!! 

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    Anderton
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    Re: Time Stretching Question 2014/08/19 10:52:12 (permalink)
    Snapping relates to the tempo, not the stretch percentage. I'd advise not paying too much attention to the calibration and instead paying attention to the duration.
     
    For example, suppose the tempo is 71 BPM. Record your part, and let it go for a little longer than just the part itself. Turn on snap and trim the clip to a certain number of measures - let's say 4 measures. Now when you speed the tempo back up, with snap on stretch the clip down to 4 measures at the new tempo (I assume you're stretching by holding down Ctrl while you slip-edit, yes? That's the easiest way to do it). It should line up exactly.
     
    However, there might be a better way to do this as that's a very wide amount of stretch - even with the offline render when you bounce to clip, the fidelity might be questionable. If you cut the clip into individual notes at the slower speed then speed up, the notes will stay on the timeline and speed up as you speed up the tempo. You'll probably have to trim the length as the notes will run into each other, but as you won't be using DSP, the audio quality will be what it was when you recorded this notes. This month's Sound on Sound has an article I wrote about this technique, however, the August 9 tip on "Faux REX Files" in my "31 Days of Tips" thread tells how to do this in an abbreviated fashion using AudioSnap. AudioSnap can do this for parts with pronounced transients like drums, but you may need to create the slices manually for finger-picking.
     
    Hope this helps!

    The first 3 books in "The Musician's Guide to Home Recording" series are available from Hal Leonard and http://www.reverb.com. Listen to my music on http://www.YouTube.com/thecraiganderton, and visit http://www.craiganderton.com. Thanks!
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    Kalle Rantaaho
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    Re: Time Stretching Question 2014/08/19 11:07:29 (permalink)
    Mojo3432
    Hello My Fellow "Sonar-ians",
     
    My question is WHY?  There really shouldn't be any extra slack in there.
    Shouldn't each increment you squeeze or stretch the audio be a the next % in value?  
    60%, 59%, 58%, 57% etc....not 60%, 60%, 60%, 59%, 59%, 59%.....
     




    Why do you think so?
    1% is only 1/100.  That is not even close to accurate enough for all purposes.
    If there is, say, 400 ticks in a beat, and you shrink it by 3 ticks...well count yourself :o)
    Per cents don't need to be full numbers.
     
     

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    Mojo3432
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    Re: Time Stretching Question 2014/08/19 11:27:16 (permalink)
    Craig and Kalle, thank you so much for the responses.
     
    So apparently I was using the wrong tool for the job as I should have been utilizing the snap tool instead of the stretch tool.  That makes sense now.  And Craig, I will definitely check out your August 9th Tip and the S.O.S. article. Thanks again for your help.  I will read up on this and give it a try.
     
    Thanks 

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    Skyline_UK
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    Re: Time Stretching Question 2014/08/19 12:30:09 (permalink)
    I've never found Sonar's time stretching any good. E.g. this week I did a guitar solo over a dozen bars or so but later decided to change the tempo of the song from 92 down to 88, as that felt better for the overall song, but I really wanted to keep the guitar solo. I highlighted the guitar solo clips one at a time, went in  the Inspector, specified stretch the audio, filled in the 'original tempo' box as 92. The result was useless - way off. Even tinkering with the 'original tempo' to try and force things to sound right didn't work. I've always had this problem in Sonar.  In Studio One such a change to audio works 100% as expected.
    If I am doing something wrong I can't see what it is!

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    #5
    Mojo3432
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    Re: Time Stretching Question 2014/08/19 12:55:34 (permalink)
    Hey Skyline,
     
    I guess that's why I didn't have the results I expected either.  I guess I just assumed the Audio Stretch tool would be what you would use to achieve this.  I wouldn't have thought about doing it with the Audio Snap tool until reading Craig's reply.  I didn't really consider measures or ticks...I was going more on the mathematical concept of 40%=40% and couldn't figure out why it wouldn't fall back in line perfectly.  Sonar is the only DAW I've ever used, so I don't really have anything to compare this process to.
     
    Haha...However, if Studio One does this as easily as I hoped it would in Sonar it may be worth keeping on hand for just such an occasion.  

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    Anderton
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    Re: Time Stretching Question 2014/08/19 14:31:20 (permalink)
    Hold on! Obviously I didn't explain this clearly enough.
     
    @mojo3432 - you're overthinking this, I'm not talking about AudioSnap, and the stretch tool works too. What I'm trying to describe is the simplest way to do things.
     
    If you have a 4-measure clip in a song with a slow tempo, when you speed up the tempo the clip's duration will be too long. If you slip-edit the end with the Smart Tool while holding Ctrl, it temporarily becomes the stretch tool. If you slip-edit while Snap to Grid is enabled for measures, then you'll "shrink" the clip to 4 measures in the new tempo. 
     
    BUT that's only part of the process. When you stretch, Sonar adopts a temporary real-time "preview" mode that sounds pretty dreadful. If you bounce the clip to itself, it renders using the high-quality Radius stretching algorithm by iZotope, and the sound is vastly superior.
     
    Make sense? If not let me know.
     
    Also. I realized that I don't know how you're slowing the tempo down in the first place. I assumed it was MIDI tracks, but maybe you're doing a premix and using stretch to change its tempo?
     
    If you're expecting a way to varispeed an entire song, that is complicated (although possible) to do in Sonar. However, slowing down a premix for a reference, playing along with it, and then speeding your part back up is simple; and with the offline rendering, you can get good sonic results. Cutting and repositioning the notes as described in the article I referenced, you can avoid any artifacts caused by the stretching process itself as there is no stretching - only re-positioning clip start times on the timeline.
     
    So there are plenty of ways to do what you want...you can even turn the clip into a groove clip so it follows tempo changes, but that's a whole other process.

    The first 3 books in "The Musician's Guide to Home Recording" series are available from Hal Leonard and http://www.reverb.com. Listen to my music on http://www.YouTube.com/thecraiganderton, and visit http://www.craiganderton.com. Thanks!
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    Anderton
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    Re: Time Stretching Question 2014/08/19 14:44:36 (permalink)
    Skyline_UK
    I've never found Sonar's time stretching any good. E.g. this week I did a guitar solo over a dozen bars or so but later decided to change the tempo of the song from 92 down to 88, as that felt better for the overall song, but I really wanted to keep the guitar solo. I highlighted the guitar solo clips one at a time, went in  the Inspector, specified stretch the audio, filled in the 'original tempo' box as 92. The result was useless - way off. Even tinkering with the 'original tempo' to try and force things to sound right didn't work. I've always had this problem in Sonar.  In Studio One such a change to audio works 100% as expected.
    If I am doing something wrong I can't see what it is!




    This may also be a case of overthinking it (and Mojo3432, this might be more helpful to you than the general description given above).
     
    1. Temporarily set the song to the original tempo at which the guitar solo was recorded.
    2. Bounce the solo to a single clip that's a specific number of measures (or beats; it's just that measures are nice, big targets for snapping). Let's say it's 10 measures.
    3. Set the song to the new, slower tempo. The guitar solo will now be too long.
    4. Slip-edit the end of the guitar solo while holding Ctrl (this turns the smart tool into the time stretch tool temporarily, as confirmed by the edge of the clip being a yellow line instead of a blue one), and snap the end to a measure boundary to it's back to being 10 measures long.
    5. Bounce the solo to itself to invoke the offline, high-quality rendering.
     
    That should do it.

    The first 3 books in "The Musician's Guide to Home Recording" series are available from Hal Leonard and http://www.reverb.com. Listen to my music on http://www.YouTube.com/thecraiganderton, and visit http://www.craiganderton.com. Thanks!
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    soens
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    Re: Time Stretching Question 2014/08/19 15:42:01 (permalink)
    As a wise old margarine commercial once warned... "It's not nice to fool with the time/space continuum", or something like that. Things can get messy when you do.
     
    Actually I've found Sonar's time stretching to be pretty awesome at times. Though not totally perfect, it has often impressed me beyond my expectations.
     
    As far as the %s go, Sonar rounds to the nearest 10th and is only a guide, not a precise measurement.
     
    Like Craig says, I find it easier to know and use the measure lines with the Snap feature. If you know the piece should start at 15:60:000 and end at 24:00:000, then stretch-n-snap it to those points, and then bounce it.
     
    Splitting and bouncing clips:
    To make splitting large clips easier you can change from "Clips" to "Audio Transients" in Track View to see where the beat marks are.
     
    You can also turn off Snap and zoom way in for precise splitting.
     
    Joining 2 clips:
    Joining 2 clips can get tedious if the wave form connection points are not perfectly aligned. This can cause "clicks" and other noises where the two are joined.
     
    To prevent this, I zoom in and find a point where the end of clip 1 lines up perfectly with the beginning of clip 2 by "slip editing", not stretching. I also prefer this point to be at the wave's vertical centerline. Once I find that point I make sure to "butt" the clip ends together with no overlap and then bounce them together. This usually works flawlessly as long as you keep the wave pattern uniform to its original shape.
     
    example:   |--___----____--_---| |--___--___---_---___-_|
     
    where "|" = clip ends and "--___----" = wave form.
     
    Steve
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    Anderton
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    Re: Time Stretching Question 2014/08/19 15:56:35 (permalink)
    soens
    Actually I've found Sonar's time stretching to be pretty awesome at times. Though not totally perfect, it has often impressed me beyond my expectations.



    In my experience, the iZotope and zPlane stretch algorithms are pretty much as good as it gets, especially in light of the need to interfere with the time/space continuum 

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    Geo524
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    Re: Time Stretching Question 2014/08/19 21:15:00 (permalink)
    Skyline_UK
    I've never found Sonar's time stretching any good.

    +1. I use Reaper when I need to time stretch a clip. It works like it should. Easily and without any artifacts.



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    Anderton
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    Re: Time Stretching Question 2014/08/19 21:38:26 (permalink)
    Geo524
    Skyline_UK
    I've never found Sonar's time stretching any good.

    +1. I use Reaper when I need to time stretch a clip. It works like it should. Easily and without any artifacts.



    Reaper lets you varispeed an entire project easily, and so does Studio One Pro. That said, I've never encountered a real-time pitch-stretching algorithm that could work with as wide a variety of program material as ones that render offline. I particularly appreciate that the iZotope algorithm used in Sonar gives a choice of bass, vocal, solo, and mixed material. Same with sample-rate conversion; check out these comparisons of artifacts from sample rate conversion for multiple programs. Unfortunately I don't know of an equivalent chart for stretching algorithms. 
     
    I have encountered a lot of people who think Sonar's stretching sucks because they don't know how to choose the right algorithm for the material they want to stretch, or don't realize stretching defaults to a real-time preview mode that does in fact suck. Not saying you guys don't know that, but it is an issue that comes up a lot. Hmmm, might make a good tip...
     
     
     
     

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    Mojo3432
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    Re: Time Stretching Question 2014/08/20 09:38:21 (permalink)
     I have encountered a lot of people who think Sonar's stretching sucks because they don't know how to choose the right algorithm for the material they want to stretch, or don't realize stretching defaults to a real-time preview mode that does in fact suck. 

     
    Agreed.  I will be the first to admit "operator error" on this one.  I didn't understand the proper way to go about achieving what I was trying to do.  I don't blame Sonar at all.  It's a fantastic DAW with all of the tools anyone could ask for.  It was simply my lack of knowledge keeping me from doing the job right.
     
    As far as the sound quality...once you "bounce to clip" my audio sounds perfect.  But that was never an issue with me anyway.  And yes...I was only adjusting the speed of my MIDI drum track.  I wasn't time stretching the entire project, only the guitar arpeggio that I'm not talented enough to play in real time. 
     

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    Kylotan
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    Re: Time Stretching Question 2014/08/20 16:49:47 (permalink)
    Anderton
    I have encountered a lot of people who think Sonar's stretching sucks because they don't know how to choose the right algorithm for the material they want to stretch, or don't realize stretching defaults to a real-time preview mode that does in fact suck. Not saying you guys don't know that, but it is an issue that comes up a lot. Hmmm, might make a good tip...



    As you saw from my other thread with the bug, I've been doing some time stretching recently using the Ctrl-drag method. How would I configure the algorithm if I wanted to bounce those clips? I know that when using Audiosnap, at least under 8.5, I could choose between various iZotope modes, but I don't see any of that appear when I just stretch things in the Track View like this.

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    Anderton
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    Re: Time Stretching Question 2014/08/20 17:13:57 (permalink) ☄ Helpfulby Kylotan 2014/08/20 17:09:24
    Kylotan
     
    As you saw from my other thread with the bug, I've been doing some time stretching recently using the Ctrl-drag method. How would I configure the algorithm if I wanted to bounce those clips? I know that when using Audiosnap, at least under 8.5, I could choose between various iZotope modes, but I don't see any of that appear when I just stretch things in the Track View like this.



    The mode still adopts whatever offline stretching mode is selected in AudioSnap...I realize, though, that's not intuitively obvious. It's something that should be added to the documentation. 

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    gswitz
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    Re: Time Stretching Question 2014/08/20 21:43:37 (permalink)
    I've watched the videos and read the books describing how to do this.
     
    I've tried it again and again on lazy Sundays.
     
    I'm mostly a hobbiest, so ... I just replay rather than changing tempo.
     
    That said, I do think it's outrageously cool what you can do with it.
     
    The most  important thing for me when working with this stuff is how to get the transients back out of my project. The size of your project can explode and saving the project can suddenly take a long time. To get the project size back down after playing with Audio Snap and Transients, save as a bundle, then save back as the project. Boom, size back to tiny.
     
     

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    Anderton
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    Re: Time Stretching Question 2014/08/20 21:56:54 (permalink)
    gswitz
    I'm mostly a hobbiest, so ... I just replay rather than changing tempo.



    I'm not letting that go by without a comment 
     
    I generally think that's a better approach. I've never re-cut a song that wasn't better than an earlier attempt. There's something about the process of learning the song the first time that translates into a more confident performance on the second go-round.
     
    For me this is most noticeable with vocals. When I cut vocals, I'll then listen to them over and over and do new vocals. They're always better. I liken this to a (very) "lite" version of taking your music out on the road and honing it in front of an audience.
     
    And frankly, "back in the day" when a song wasn't working, the pros would know when to cut their losses and just start over. Many of the songs that became classics didn't start off the way they ended, "Sympathy for the Devil" being a prime example because its evolution was captured in a Jean-Luc Godard film. There wasn't this ethic of "if it has problems, we'll fix it." 
     
    Don't get me wrong: I like having fix-it tools to take something from 95% to 99%. But if the tempo itself is off, that tends to influence everything from the feel to the parts themselves. Recutting respects the needs of the new tempo.
     
    Damn, I can be wordy sometimes 

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