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Topic: Audacity/SoundBlaster - Recording Lag (Read 7578 times) previous topic - next topic
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Audacity/SoundBlaster - Recording Lag

Hey, I know this place is one of the more knowledgeable sources of digital audio info, I was hoping someone might be able to help me out with this problem. I already tried the Audacity forums, pretty much the only advice I got was to get a new sound card, which I don't really have the money for.

I've been recording with Audacity for at least a year or two now and I haven't had too many problems, but lately I've had trouble with recording things. Often when I record one track of something and then record another track over it, they'll not only be misaligned from the start, but further in they'll move further and further out of sync. I'm recording using a Creative Sound Blaster Audigy 2 ZS.

Here's a sample of what's been happening that I just made. I recorded my metronome by plugging it into the line-in spot, then plugged the cable into the headphone jack to record it again as it played back. The first track is in the right channel, the second track is in the left channel. Even after only 15 seconds or so you can tell that they're shifting.

http://www.mediafire.com/?enyt0lrtbng

Does anyone have any idea what might be causing this or what I can do to go about fixing it? Are there more specifics that I need to give? Thanks in advance, this has really been frustrating me.

Audacity/SoundBlaster - Recording Lag

Reply #1 –
That's a weird one!  I could understand constant delay*, but the drift is strange...

My guess is that the guys at the Audacity forum are right...  I think it's your soundcard.  Are you using 2 different soundcards, or an external device with along with an internal soundcard/soundchip?

Here's the thing - The timing is determined by the soundcard's clock (oscillator). If you record at 44.1kHz, but it's not really 44.1kHz, you can get problems.  Here's the weird part - Usually the same oscillator is used for recording and playback, so you usually won't notice a problem until you play-back the file on a different computer, or until you make a CD. 

--------------------
* A (constant) recording and playback delay is normal.  Because the CPU is always multitasking, the audio is written and read into buffers.  A buffer is like a storage tank or a long pipe can keep data flowing, but it also acts like a delay. 

The operating system is always multitasking, because it's always running background tasks even when you are running only one application.  Of course, recording and playing-back at the same time requires multitasking as the data bus & hard drive switch rapidly between reading & writing.

You can "record" data into the recording buffer at a constant rate.  When the buffer is almost full (and when the operating system allows the recording process to use the data bus) a burst of data is transfered from the buffer to the hard drive.

The same thing happens during playback.  A burst of data fills-up the buffer.  When the buffer is about full, data starts streaming out of the playback buffer at a constant rate.  When the buffer is almost empty (and when the operating system allows the playback process to use the data bus) a burst of data re-fills the buffer.

Some software allows you to tweak the latency (delay).  When you do this, you are really adjusting the buffer size.  With a faster system (or with less multitasking) you can get-away with a smaller buffer.    Most professional soundcards & applications use ASIO drivers which are designed for low-latency.

Audacity/SoundBlaster - Recording Lag

Reply #2 –
I am using two different soundcards, an external Sound Blaster Audigy is plugged into the Sound Blaster Audigy 2 ZS, which is the internal fixture.

Are you suggesting that I try and adjust the latency setting to try and see if I can at least reduce the problem at all? Audacity does offer that option; right now it's set at 100 milliseconds to buffer and 0 milliseconds for latency correction. How much should I increase it by to see if it'll give me some sort of result?

Also, regarding what you said about sampling rates; someone on the Audacity forum said that the Audigy's native sampling rate is 48kHz, so I set it to that in the quality preferences of Audacity. The same thing still keeps happening though.

Thank you very much for your advice, I think I'm starting to figure this thing out a little bit but I feel like eventually I'm just going to have to end up buying a new computer.

Audacity/SoundBlaster - Recording Lag

Reply #3 –
You're not alone.  I have the very same problem with my old Santa Cruz.  It happens with both Audacity and Audition.  I noticed that rebooting helps a little, but not much, and the problem quickly comes back after a few tracks have been recorded.

This is one of the most annoying problems I've faced while recording.  It makes keeping time while playing along to overlapping tracks very difficult, especially when changing time signatures frequently.

Audacity/SoundBlaster - Recording Lag

Reply #4 –
Yeah, it's extremely frustrating. I always want to record new songs but this problem's pretty much got me stuck in place.

Audacity/SoundBlaster - Recording Lag

Reply #5 –
Quote
I am using two different soundcards...
Bingo!  One of the soundcards has an incorrect clock frequency.  This is not "user-repairable".  The only way to repair it is to replace the crystal on the soundcard.  At this point, we don't know which soundcard is causing the problem... we just know that they don't "match".  It's actually possible (but unlikely) that one is fast, and the other is slow!  You might need a 3rd soundcard or another computer to determine which soundcard is off.

Quote
..the Audigy's native sampling rate is 48kHz
  I don't think that's the problem.    No matter what the "native" rate is, it should be able to derive all of the normal sample rates required to play/record a file with any "standard" sample rate. 

Quote
Are you suggesting that I try and adjust the latency setting
  No.  That only affects the constant delay, not the "drift".  Sorry, I got off-track with that.  For example, you could live with a 10ms constant delay, but you can't live with a delay that that grows by 10ms every second. BTW -  I'm sure you are getting a pitch-shift along with the tempo-shift.  Sometimes this is a worse symptom for a musician.

BTW -  I'm sure you are getting a pitch-shift along with the tempo-shift.  Sometimes this is a worse symptom for a musician.

P.S.
So, if one of the soundcards has the ability to play and record at the same time, you should be OK, if you just use that one soundcard.  (You will still get a pitch/tempo shift when you play back on the other soundcard.  And, if you use the "bad" soundcard for this, you will get a pitch/tempo shift when you play-back on a good computer or if you burn an audio CD.

P.P.S.  If you can hear the pitch-shift, I thought of a way you can determine which soundcard is bad -
-Record a note (or a short bit of music) with each soundcard. 
-Burn both samples to a CD.
-Play-back the CD on a stand-alone CD player, and you should be able to determine which sample is off-pitch.
 

Audacity/SoundBlaster - Recording Lag

Reply #6 –
I think it's most likely the internal card that's causing the problem; I've only had the external card for a few weeks and the problem started well before that. Is there way I can circumvent the internal soundcard, maybe by plugging the external into a different part of my computer? Thanks again for your help.