Subject:A related problem with digital audio

Posted by: frogman06

Date:6/5/2007 12:07:52 PM

I need some advice on a problem im haveing .
My Alesis HD24 is doing something funny.
It is not playing back correctly .
I recorded a click trk from acid into the HD useing the inturnal clock settings.
When i line up the recording of the click back into acid it drifts out of sync with the metronome.
I know this is a problem with the HD not Acid but im hopeing i can get some input from the forum.
I have synced audio by eye & ear this way before & it works.
The HD took a fall about 1 yr ago but
Ive used it this last year and dident notice any thing wrong with the audio.
Then i tryed to lock up video of a band with the audio i recorded on the HD togeather in Acid.
It will not sync.
I recorded a click into the camera , put it into Acid and it locked up to the metronome fine.
What would cause the audio to drift???
Why does it get more out of sync over time???
With digital shouldent it stay consitant over time and not drift more
as the audio plays????
Again i have locked video and audio this way in acid before so i know it works.
Is this a word clock issue in the HD ?????
What controls the clock ??????
Can it go bad ???
Any help is most appreciated
thanks
Frog

Subject:RE: A related problem with digital audio

Reply by: pwppch

Date:6/5/2007 1:21:07 PM

The most likely cause is different clocks.

How are you assuring that your sound card and the Alesis are using a common clock source?

Peter

Subject:RE: A related problem with digital audio

Reply by: frogman06

Date:6/5/2007 10:45:04 PM

I recorded the audio analog.
No word clock or sync was used.
Im not syncing the HD to my puter in any way.
The camera records video & audio, at the same time i record audio on the HD useing the anolog inputs. I then put the audio from the HD and the audio & video from the camera into Acid.
I then sync the HD audio to the audio track of the camera by eye & ear.
I have done this many times.
It is not sample accurate but better than frame accurate.
It works.
It will not work now.

Thanks
Frog

Subject:RE: A related problem with digital audio

Reply by: pwppch

Date:6/6/2007 6:17:24 AM

My point is that if the clocks are not exactly the same between the two units, then there can be drift.

If the sound card is running at 44.150kHz and the external "gear" is at 44.102 kHz, then there will be drift.

I cannot explain why it use to work and now it does not.

Peter

Subject:RE: A related problem with digital audio

Reply by: Iacobus

Date:6/6/2007 9:35:39 AM

Frog, I noticed that the Gina24 and the HD24 both have ADAT optical I/O. Have you tried sync'ing the two together that way? (You should do it this way. You'd save a boatload of time rather than having to sync manually.)

Iacobus

Subject:RE: A related problem with digital audio

Reply by: frogman06

Date:6/6/2007 10:26:40 PM

I port over the files directly from the HD removable hard drive.
No sync is needed.
Im not shure im explaneing this very well.
Thanks for all the help.

Subject:RE: A related problem with digital audio

Reply by: frogman06

Date:6/6/2007 10:29:56 PM

Shouldent the drift remain constant between the two ??????
The difference at 10 seconds should be the same as the diffrence at 1min .... right?
Frog

Subject:RE: A related problem with digital audio

Reply by: Chienworks

Date:6/7/2007 4:13:51 AM

No. The point is that audio recorded on different devices may play back at different speeds when moved to other devices. So, even if you get the sync perfect at one point, the drift can cause the sync to change, or drift apart, over time.

Subject:RE: A related problem with digital audio

Reply by: pwppch

Date:6/7/2007 12:00:11 PM

No, sync is still needed.

Just because the file says it is 44.1 kHz, the actual data written to the file could be at a different sample rate.

So, if the HD Removable drive writes a file that tells ACID it is 44.1 kHz, but it really is 44.105 and then ACID loads this in and the hardware on the PC is running at 44.050 kHz, then there will be drift over time.

The way this is typically solved in the real world is to use a master clock source for everything always.

Run all external hardware (including your sound card) off of the same common clock .This way you are assured that everything you record/playback will always be at the same sample rate.


Peter

Subject:RE: A related problem with digital audio

Reply by: frogman06

Date:6/8/2007 9:58:41 PM

Thanks for the input .
This is why i love this forum....
Im not shure how i could do that..
I record live {away from my puter } with the Hd 24 then dump the trks into Acid to mix.
My camera {sony} he he he, syncs fine when i dump the audio from it into Acid.
Ive allso synced audio from a cd boom box recorded with the camera mics on a remote music shoot back to the final music mix in Acid.
Frog

Subject:RE: A related problem with digital audio

Reply by: Iacobus

Date:6/11/2007 10:04:46 AM

That's what I was afraid of. :) I figured you used the HD24 remotely from the rest of the system.

Hmm. For giggles, is the HD24's sample rate set at the correct sample rate? (p. 35 of the HD24's manual mentions how to change it —with a simple press of a button.)

Still, I thought that despite the sample rate mismatch, ACID Pro would resample on the fly based upon the overall ACID project's sample rate? (Kind of like how it treats 16-bit samples in a 24-bit ACID project?) I know not all DAW software does this for you (which is why it would be important to match sample rates exactly).

Do you have Sound Forge, Frog? It will tell you exactly what the sample rate is from recordings made by the HD24. (ACID Pro can do this too, but it's quicker in Sound Forge.)

Subject:RE: A related problem with digital audio

Reply by: Chienworks

Date:6/11/2007 10:32:36 AM

Even still though, suppose the recorder was set for 44,100 but actually recorded at 44,100.3, which is not at all unlikely. The file would be marked as 44,100 and ACID would assume it was. That means that ACID will play it back at 44,100 instead of 44,100.3 and by the end of an hour that track will be about 1080 samples behind, nearly 1/40 of second. OK, that's not much. But suppose the actual recording was at 44,107.2 instead. Still only 0.0163% error, but this time after an hour the error will be over half a second, around 25,920 samples behind.

Unless the recording device writes the actual sample rate to the file instead of the rate it was supposed to be using even ACID's resampling can't correct for it automatically.

That's the drift problem that occurs when the different devices' clocks aren't externally synced to each other.

Subject:RE: A related problem with digital audio

Reply by: frogman06

Date:6/15/2007 12:17:06 AM

File was recorded at 44.1 on the HD useing the anolog ins.
The files im useing are mostly 4 or 5 min long.
It always has worked before on this same mechine and acid.
It drifts after about 20 -30 sec.
That is mighty quick.
Md do you have a HD ???
You seem very knowledgable about it . :}
Frog
.

.

Subject:RE: A related problem with digital audio

Reply by: Iacobus

Date:6/17/2007 9:21:44 AM

No, I don't have an HD24. (Most of the info I've given has been from the downloadable manual from Alesis' site.) ;)

The files are 4 to 5 minutes long? Hmm. Files that long are (usually) seen as one of two file types by ACID: Beatmapped or One-shot.

One-shots are not stretched by ACID in any way, so you get a "what you hear is what you get" approach.

Beatmapped is another monster altogether. If the track doesn't strictly follow a specific tempo, there can be problems.

Are the tracks in question being imported as One-shots? If not, have you tried switching them to One-shots?

Subject:RE: A related problem with digital audio

Reply by: frogman06

Date:6/17/2007 6:07:16 PM

there 1 shots .
I also tryed syncing in Vegas .... same problem.
It must be the hd's clock is messed up.
The problem is when it records its running to slow by a lot i think.
thanks
Frog

Subject:RE: A related problem with digital audio

Reply by: Iacobus

Date:6/21/2007 12:45:03 PM

If Vegas is doing it too, there's definitely something up.