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Changing tempo by % to maintain tempo map?

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Hi all, 

Weird request -- I've created a tempo map for a set of audio files that I captured at 1/2 speed, and now I want to double the effective tempo of my audio regions. 

I see that the Time and Pitch Machine allows one to change tempo by a percentage figure, albeit while also requiring a pitch change of a non-zero amount -- annoying, but I'm finding that while I can compensate for the pitch change the overall effect on my audio tracks removes some transient material, at least on the default setting of Percussive. Before I try any of the other algorithms I thought I'd ask here to see if there's a simpler way I'm overlooking.

Crazy Back story: I'm revisiting a recording I did 40 years ago on a 4-track cassette deck, which I no longer have, so I've captured the tracks 2 at a time and at half-speed from a home stereo cassette deck and now I'm trying to align and correct them. Pitch is solved with Logic's track transpose feature, time reversal is solved for tracks 3 and 4 at the audio file level, and since one of the original tracks contained a metronome I was able to easily make a matching tempo track by applying region tempo to project tempo. Since the tempo is variable I can't simply double the tempo control to return to the original tempo.

Seems like there should be an easy way to do this -- what am I missing?



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44 minutes ago, Atlas007 said:

How about Varispeed?

Thanks, that's certainly easier! It also sounds better than the default setting for Time and Pitch Machine, though I'm still getting some smearing on the metronome track. Marking your post as the solution because it answers my stated question, but I think I'm going to play bit more to see if I can find a method that maintains the attack of the metronome transients. Thanks, again!

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Here's what would be my strategy for this:

First, a couple of facts and assumptions:

- Since the original tape speed was twice as fast, the time and pitch (t+p) of the audio at transfer time will be twice as long and one octave down
- In addition to this, there will be considerable t+p drift throughout the material due to the poor speed calibration and stability of both the recording tape machine and the transfer tape machine and also due to tape stretching
- Only two of the four tracks can be transferred at a time, so there will be additional drift from the player between the two passes of two tracks each
- Original tracks 3-4 will sound backwards after transfer

So, all these things considered, there's no "easy way to do this", but still doable. Here's the procedure:

- Thoroughly clean the heads of the playback tape machine with Isopropanol (pure alcohol), let it dry completely
- Record pass 1 as a stereo Track into Logic
- Flip over the tape and record pass 2 as a second stereo Track into Logic
- Reverse the entire pass 2 in the Audio File Editor, so original tracks 3-4 will sound forward again
- Move passes 1 and 2 so that their first downbeat aligns perfectly with one of Logic's barlines (hoping that something reasonably percussive will be on both passes 1 and 2)
- Trim both Regions in the Main window so both start exactly on that downbeat
- Beatmap to Region 1 (the one that contains the click), like this:


Now we have a Tempo Map that matches the slow transfer speed and the drift of both recorder and player in Region 1

- Ctrl-click Region 1 (not Region 2!)> Tempo>Write Project Tempo To Audio File
- Enable Flex Speed on Track 1 with Region 1. It will change colour, but stay put
- Go into the Tempo List Editor, remove all but the first Tempo Event and set that to the original tempo of the song. If you don't know what it was, look at the first couple of Tempo Events, then double and round that number. If it's 59.454 bpm, we can safely assume the original tempo to be 120bpm

Now we have changed Region 1 to correct pitch, tempo and length

- Enable Flex Speed on Track 2 with Region 2. It will change colour, and shrink to *roughly* the same size as Region 1, but it will still have the drifts of recorder and player, making it run out of sync with Region 1
- Adjust the end of Region 2 so that its downbeats roughly line up with Region 1 and Logic's grid
- Using Flex Markers, pull each downbeat of Region 2 to Logic's grid, like this:


Now we have changed Region 2 to correct pitch, tempo and length

- Duplicate both Tracks 1 and 2 (New Track With Duplicate Settings) with their Regions 1 and 2
- With a long click on each Track's Mono/Stereo Button, select original tracks 1-4 for the resulting four Logic Tracks

Now we have four independent mono Tracks from the four original tracks, all perfectly in time, in tune and aligned to Logic's grid for further mangling.

Edited by fuzzfilth
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14 hours ago, fuzzfilth said:

Here's what would be my strategy for this:


Now we have four independent mono Tracks from the four original tracks, all perfectly in time, in tune and aligned to Logic's grid for further mangling.

Thanks much for the very detailed outline -- with screen movies, no less! And you are so right about cumulative time and pitch drift -- my mix of this tune was 10% sharp but interestingly enough, the master was played back at the original speed, albeit half-time, checked by an a-440 tone I recorded before the intro. 

I ended up letting Logic create a tempo map from my first stereo pair, which worked pretty well as track 1 was actually a metronome recording, adjusting the other tracks to match, but I did end up with transient clipping of that metronome beat and the paired percussive melody. I haven't gone back to the project because my main goal is to recreate the tune but needed to tease out chords that were difficult to identify in the mix version due to combined pads where one was tuned to 5ths, confusing my ear. 😉

Your post would be a great resource/tutorial to stash somewhere for posterity -- thanks again!

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17 hours ago, exmachina said:

Your post would be a great resource/tutorial to stash somewhere for posterity -- thanks again!

That can be said about the vast majority of fuzzfilth's posts, so much detailed information. You are a fountain of knowledge Christian and I have learned so much from you over the years.

Thank you,


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