tracking with two digital multi track recorders

V

VirtualSamana

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I am tracking drums and need more inputs than my Tascam US428 interface will allow. I am thinking of adding another two by recording simultaneously with my Korg PXR4. After I download the PXR4 tracks to my computer I will line up the wave froms on my DAW.

has anyone tried this with success or have any suggestions.
 
You will want to sync them up with midi time code if possible. Otherwise a little bit of drift is almost guaranteed.
 
It would be interesting to see how far they do drift. Easy to test anyway.
I see the Korg runs at 32kh. Can you import these into your pc (presuming 44.1 there?) or will you have to record them in analog in a separate pass? More drift?
 
I doubt if midi time code is as accurate as the individual clocks in each digital recorder. Midi itself is considerably slower and more sloppy than the clock rates of digital recorders. It would be a waste to mess around with midi time code, in my opinion.

Just line up the audio files and see if they phase at all. There will be some drift, but it should be very small. The only way to know if it works is to try it, and that's fairly easy. Just make sure that each recorder is set to the same sample and bitrate, like 16bit/44.1k, for example.
 
SonicAlbert said:
I doubt if midi time code is as accurate as the individual clocks in each digital recorder. Midi itself is considerably slower and more sloppy than the clock rates of digital recorders. It would be a waste to mess around with midi time code, in my opinion.

Just line up the audio files and see if they phase at all. There will be some drift, but it should be very small. The only way to know if it works is to try it, and that's fairly easy. Just make sure that each recorder is set to the same sample and bitrate, like 16bit/44.1k, for example.
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That's what I was going to say... I'd think the clocks would be better than anything to do with midi. If the recorders have the option do use an external clock source, might be a good way to go. or if one can be the master clock and the othe the slave...dunnoo if those recorders can do stuff like that, but that would keep it from drifting.
 
SonicAlbert said:
I doubt if midi time code is as accurate as the individual clocks in each digital recorder. Midi itself is considerably slower and more sloppy than the clock rates of digital recorders. It would be a waste to mess around with midi time code, in my opinion.

Just line up the audio files and see if they phase at all. There will be some drift, but it should be very small. The only way to know if it works is to try it, and that's fairly easy. Just make sure that each recorder is set to the same sample and bitrate, like 16bit/44.1k, for example.
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Is this your opinion based on having actually tried it or just guessing? Everytime I've tried to sync multiple recorders without sync they always drift. Even two soundcards in the same computer will drift if they don't have a way of syncing to each other.

If it wasn't neccessary they wouldn't have invented SMPTE or MTC. MTC is plenty accurate enough to sync. That's why they made it. It is as accurate as the master clock which is the whole idea behind sync. Both units follow the same clock.

Unless your recorders are timed with a nuclear clock they will drift. Any drift is too much. It's not just a timing issue but also a pitch issue. Even if the beat seems close there will be an obvious flange type effect as time goes on.
 
mixsit said:
http://www.korg.com/gear/info.asp?A_PROD_NO=PXR4
Uh guys, I don't think this thing is going to chase house sync.


This could be the deal killer. On some vocals, guitars, a few ms, no big deal. But on mixed percussion it could be.

Still, try it and see. :)
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The only way it would have a chance of working is if both recorders weren't recording the same source. If it was drums on one recorder and direct bass or guitar on the other then it could be made to work. Both recorders on one drum kit is going to sound pretty weird.
 
TexRoadkill said:
Is this your opinion based on having actually tried it or just guessing? Everytime I've tried to sync multiple recorders without sync they always drift. Even two soundcards in the same computer will drift if they don't have a way of syncing to each other.

If it wasn't neccessary they wouldn't have invented SMPTE or MTC. MTC is plenty accurate enough to sync. That's why they made it. It is as accurate as the master clock which is the whole idea behind sync. Both units follow the same clock.

Unless your recorders are timed with a nuclear clock they will drift. Any drift is too much. It's not just a timing issue but also a pitch issue. Even if the beat seems close there will be an obvious flange type effect as time goes on.
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I'm not guessing. And for the record I use SMPTE, MTC and a master word clock in my studio, and am familiar with all of them.

Look at the resolution of MTC and SMPTE and then look at the resolution of a digital audio recorder. SMPTE/MTC is designed to sync with an accuracy of 24-30 frames a second, while digital audio recorders are designed to an accuracy of 44,100 frames (samples) a second at a 44.1khz sample rate, for example. You decide which is more accurate.

SMPTE/MTC at 30 frames a second is not accurate enough to prevent the tiny drift that will occur at 44,100 frames a second or higher. You can have sync at 30 frames and still have drift within the 44,100 frame rate. Furthermore, a digital recorder will not drop or add frames to "catch up" to SMPTE. It will keep chugging along at exactly 44,100 frames a second (at 44.1k). So any drift that is there will still be there, because the crystal is not synced to the crystal of the other digital recorder.

If you want to get accurate video sync, you need to use a black burst generator, and then sync your time code generators and master word clock generator off that. Having digital recorders locked to freewheeling SMPTE time code isn't going to be accurate at all, in terms of controlling the tiny drift of the digital recorder.

If you have a SMPTE/MTC generator locked to a master clock, then it should be accurate. But that's because of the accuracy of the master word clock, not anything inherent in MTC or SMPTE. And in that case the digital recorders should be locked to the master clock *and* SMPTE/MTC if you need it.

SMPTE sync and word clock sync are really two different things.
 
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Ok, I'm not gonna say I know everything there is to know about MTC sync, but let's say I know more than the average bear. I've used it very successfully on a few occasions, and have never had a bad experience with it. The flange issue is not a problem as long as you observe one rule - don't split stereo tracks or tracks with related bleed across synced machines.
Now here's where I'm going to go out on a limb a little bit, because I don't know the exact code implimentation inside the sequencer, but I've written some sync code. MTC sync certainly does not replace the 44.1K clock. MTC sends a stream of quarter frame messages, each of those being sort of a clock tick, so at 30FPS, it's really 120 quarter frames per second. It takes 8 of these quarter frames though to make up a complete positional message, so it's only 15 times per second that it really knows exactly where it's supposed to be. But as a matter of practicality, it doesn't need to know absolute position more often than that. The 120 QFPS gives it a high enough resolution clock to chase, and yes, the operative word is chase. The slave chases the master, making tiny little adjustments as at marches on to it's own 44.1K clock, unless word clock is employed. Some software even let's you determine how fast it corrects.

A big consideration here is that most projects don't get recorded in one pass, so what are you gonna do without sharing positional information and MMC (Midi Machine Control) commands when it comes to SPPs and punch ins, let alone just fast forward and rewind.
 
Thanks for all the suggestions guys. The PXR4 records at 16 bit 32khz and compresses the file in mpeg1 layer 2 format. So I have to convert it to 16bit 44 khz wave format before inputing it to my sequencing software. I am going to try it and let you know how it goes. I am using the 4 inputs from my audio interface to mic the overheads, snare and kick. The PXR4 will handle the snare bottom and toms. If it sounds worse with these two tracks i can just forget about them. Also the song in this case is a straight ahead rock number where the drums can be looped. I don't expect to use a drum clip that is longer than 45 seconds. Not sure if this will lessen the effect of drift or not.
 
Neither of these units has word clock I/O. The Korg doesn't have a digital input at all, so it would be impossible to sync it to WC. The Tascam has a SPDIF input, which you could use to sync it to an exgtenal device with a SPDIF output, but I don't think that's really an option or needed in this case.
 
well, it would definately keep it from going out of phase, I think....I'm really kind of wondering how big of a difference it'll make on a normal song tho, anyway. I can't imagine, unless there are something in the way of hours of recording that it would be anything approaching noticable.
 
If the original question is about recording 45 seconds of audio at a time, then I don't think drift is an issue at all. It would certainly be better though if each recorder were running at the same sample rate.
 
Most of the Roland DAWS will synch to an external time clock, or provide the time clock to external units. I know my VS1680 will, because I have done it. Used VS1680's are very cheap now on ebay.
 
I gotta tell ya, I've done a lot of matching of digital audio from video with standard multitrack digital audio from multiple sources, usually for hour-long DVDs of events like corporate events, seminars, weddings, etc., most of it frankly without a house time code to keep it all together, and have never in the 10 years or so that I have been doing this kind of multitracking in digital had a problem with noticable drift whatsoever. And that's with hour-long audio tracks; the chances of finding such a problem within a three minute song track are microsocpic if your gear works to spec.

Drift is an issue with analog sources where motor speed and tape stretch and such are much bigger issues, but I've never encountered a digital-to-digital drift issue unless the local clock is downright broken.

The big advantages to master clocking in digital are not control of drift, local clocking is accurate enough where a drift rate between clocks of a couple of samples an hour is humanly unnoticable and technically insignifigant, IME. Rather, one likes the master clocking in digital order to synchronize samples and control jitter for refinement of sound quality (and even that idea has it's controversy), and to apply a common timecode signature across platforms making the post production work much easier. But drift? Not in my experience.

G.
 
VirtualSamana said:
Thanks for all the suggestions guys. The PXR4 records at 16 bit 32khz and compresses the file in mpeg1 layer 2 format. So I have to convert it to 16bit 44 khz wave format before inputing it to my sequencing software. I am going to try it and let you know how it goes. I am using the 4 inputs from my audio interface to mic the overheads, snare and kick. The PXR4 will handle the snare bottom and toms. If it sounds worse with these two tracks i can just forget about them. Also the song in this case is a straight ahead rock number where the drums can be looped. I don't expect to use a drum clip that is longer than 45 seconds. Not sure if this will lessen the effect of drift or not.
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I for one am now curious as hell. :D How about running a little test? Maybe just the both of them picking up some music off a speaker?
 
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