Two Separate Digital Recorders Can't Be Sync'd
- Thread starter Elmer23
- Start date
ashcat_lt
Well-known member
"Time stretch" is the wrong solution. "Vari-speed" will work better.
Each machine recorded (say) 44.1K samples per second, but they didn't agree on how long those seconds were. Now you're playing them back from yet another machine which probably doesn't agree with either of them, which means that neither will play back at exactly the same rate it was recorded, but one will play back faster than the other. You need to slow it down with all with the pitch shifting that entails in order to really get them in sync and in tune with one another. Time stretching without pitch change is a form of re-synthesis and will just mess it up worse.
This is pretty easy in Reaper by alt-dragging the end of the item until it actually lines up. You have to make sure that "Preserve pitch..." is disabled for the item, and it helps to trim each item to start on the clap at the beginning, line them up exactly, and then glue them each or else vari-speeding will move both claps, and you'll be going back and forth re-aligning the beginning every time you try to adjust the end.
This is easier with digitally recorded stuff because while they might not agree between units how long a second is, they will all be pretty consistent internally - it won't drift or wobble like tape or other analog media might. Analog wow and flutter make it damn near impossible to really re-synch things like this, but with digital it can work fine.
Each machine recorded (say) 44.1K samples per second, but they didn't agree on how long those seconds were. Now you're playing them back from yet another machine which probably doesn't agree with either of them, which means that neither will play back at exactly the same rate it was recorded, but one will play back faster than the other. You need to slow it down with all with the pitch shifting that entails in order to really get them in sync and in tune with one another. Time stretching without pitch change is a form of re-synthesis and will just mess it up worse.
This is pretty easy in Reaper by alt-dragging the end of the item until it actually lines up. You have to make sure that "Preserve pitch..." is disabled for the item, and it helps to trim each item to start on the clap at the beginning, line them up exactly, and then glue them each or else vari-speeding will move both claps, and you'll be going back and forth re-aligning the beginning every time you try to adjust the end.
This is easier with digitally recorded stuff because while they might not agree between units how long a second is, they will all be pretty consistent internally - it won't drift or wobble like tape or other analog media might. Analog wow and flutter make it damn near impossible to really re-synch things like this, but with digital it can work fine.
hhmm. I'm reading up right now about syncing DAW's using SMPTE time codes. Not sure if word clock or SMPTE would be better. On one of my puters the DAW i'm using can be set to master or slave. On computer number 2, not sure, I'm reading up on that now. Computer 1 is my creative force DAW and 2 is my recording powerhouse DAW (kind of like pro-tools, but more creative and without the glitches). Recording at 192 khz would be nice, less latency, but that pushes my computers pretty hard. The reason I mention SMPTE is for future reference to maybe sync up to a video device. I've been at this stuff for quite a while and still learning. I'll get back on this, just need to read up, and tweek things and see what i can do. Maybe word clock may be the best way to go???
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garww
New member
You have to test it. I think wordclock is just a analog signal generator
bouldersoundguy
Well-known member
Wordclock and SMPTE are different things. Wordclock locks two or more DACs/ADCs together sample by sample. It's not timecode. It won't tell one DAW where in the timeline the other DAW is. It's just a pulse signal. SMPTE is timecode, it indicates a specific time in the timeline but doesn't sync the wordclocks precisely. SMPTE is primarily for film and video work.
I had a chance to put Audacity's 'Change Tempo' effect to use on one of the tracks, hoping to making it exactly the same length as the other, but with no success. (I assumed 'Change Tempo' is the equivalent to Reaper's 'Varispeed' capability.)
I imported one track into Audacity, pasted the other below it, selected one of them, entered the 'Change Tempo' menu and set the new length to match exactly the other. After about an hour of processing, the selected tracks couldn't be synced, as drift was still evident. I've never used the function before, so it might be I was doing it wrong, or that the two functions are not equivalent after all.
My next experiments in software syncing are going to be a bit more scientific than this, maybe even with a remote to start recording on both machines simultaneously (if I can get one compatible with both machines).
It also appears that the drift I'm seeing is not linear or even constant (a bit either way here and there, with the net drfit being about three seconds by about 02h20m — which would entail custom editing specific segmemts of the recordings. But two hours was much too long to begin with.
It's too bad Reaper isn't available for Linux...It's solved a lot of problems for a lot of users. But Linux is what I'm stuck with (I got a modded Raspberry Pi with a better DAC for audio editing/listening because I like fanless computers when listening), and Audacity is the only decent audio editor available on that platform.
It also looks like I should be using the Zoom as a nexus for multiple microphones, instead of using separate and unconnected recorders, a setup which leads to problems like this one.
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ashcat_lt
Well-known member
I know nothing of Audacity, but "change tempo" sounds to me like some form of resysnthesis, which can't work. Also both tracks would need to start and end at exactly the same spot for setting the lengths equal to begin with.
I'm almost curious enough to see if Reaper really could do it. I've done similar things in the past with reasonable results.
But yeah, recording everything to one machine solves the problem.
I'm almost curious enough to see if Reaper really could do it. I've done similar things in the past with reasonable results.
But yeah, recording everything to one machine solves the problem.
Farview
Well-known member
Change tempo is the same as time stretch. Vari-speed sill change the pitch as well, which is exactly what you want and will be linear.
The problem with time stretch and change tempo is that it works to keep the audio sounding the same. So it is stretching and pitch shifting, while it is trying to keep the transients in place and natural. There is no way to do that without varying the timing within itself. So it will always be phasey, even when compared to another track that has gone through the same process (like two overhead mics on separate tracks)
Vari-speed simply changes the playback speed without doing anything else. This is the only way to sync up those two tracks.
Yes, recording multiple mics to the same machine solves all your problems.
The problem with time stretch and change tempo is that it works to keep the audio sounding the same. So it is stretching and pitch shifting, while it is trying to keep the transients in place and natural. There is no way to do that without varying the timing within itself. So it will always be phasey, even when compared to another track that has gone through the same process (like two overhead mics on separate tracks)
Vari-speed simply changes the playback speed without doing anything else. This is the only way to sync up those two tracks.
Yes, recording multiple mics to the same machine solves all your problems.
I knew someone was going to point that out
I was going for a walk and just decided: 'What the heck.' It was almost ready by the time I got back...I've been thinking about giving Ardour a try. It's too much program for what I need, and I haven't been able to find a version compiled for ARM chips. Even Audacity is much more than anything I'd ever need!
