What causes these audio artifacts?

farss wrote on 12/19/2005, 2:14 AM

I'm transfereing two DAT tapes and I'm hearing these odd artifacts. Not my gear for sure and I;ve heard the same thing in off air broadcasts too and it bugs me becuase i don't know how they happen.
Best way I can describe the effect is like a very poor digital rendition of a plate reverb that comes and goes, mostly seems to affect low level portions of the audio. I suspect it's just lousy A->D converters that have poor comb filters as the effect almost sounds like phasing.
Only reason I ask is this job is for a new client who'se also rather prominent and if they ask why it sounds like it does I'd like to be able to baffle them with science. And yes it's going into a Mac system and they know the transfer is being done on a PC :)
Bob.

Comments

bakerja wrote on 12/19/2005, 7:25 AM

Sounds like excessive digital compression. High frequencies swirling?

Spot|DSE wrote on 12/19/2005, 7:39 AM

Clocks set identical on the two? Recompressing anything?

VOGuy wrote on 12/19/2005, 9:16 AM

Hi Bob,

Usually, when you get this kind of problem, it's due to differences in the left and right channels, causing cancelling of portions of high frequencies when the channels are combined (or "summed") together. The "summing" can occur anywhere, including your own ears when hearing both the left and right channels simultaneously.

If you are copying through an analog link, sometimes the channels are blended at extemely high frequencies due to aging of capacitors in one of the recorder's power supplies.

I haven't had direct experience with this, but I've heard that many DAT machines had error correcting systems, which repeat segments of audio when there is a large enough tape dropout.

Also, some portable DAT machines created some sort of ultrasonic frequencies somwhere which would be filtered out in the a/d process, but which would "beat" or "hetrodyne" with ultrasonic frequencies in the audio, causing a "whooshing" sound. Again, this is hearsay, but it might be a cause.

I've always disliked DAT, even though a few years back, I earned a small fortune re-recording voiceovers originally recorded onto DATs which later became unplayable.

-Travis

farss wrote on 12/19/2005, 1:50 PM

Brain dead Bob!
When I was playing the captured audio back I still had the 410 clocking from the deck. Switching back to internal clock artifacts are gone.
Which is kind of odd or not?
It would seem that the 410 does something odd when being told to use the SPDIF clock. If I'm recording to/from SPDIF everything locks to the SPDIF clock BUT if there's no data going up/down the lightpipe it doesn't cause Vegas to lock to the same clock and hence the slight aliasing.
Easy enough to deal with when you know but when you forget....
Bob.

Spot|DSE wrote on 12/19/2005, 2:21 PM

Well...if having clocks mess you up is related to "Brain dead," then call me brain-dead too, because clocks often mess me up. We have a house standard, but when things come in off-standard and clocks need to be adjusted, it's commonly forgotten to reset them.