bizarre crackling distortion

[InjuredEar]

I was doing some faux mastering today and came across some crackling distortion that wasn't present in the source material.
I was working at 88.2/24 bit with some upconverted material (formerly 44/16)

I created a new session at 44/16, re-imported the audio (from the original 44/16 stereo wav files) and listened to the track on it's own (no other tracks in the session, no plugins)
the section in question had no distortion, but if I gave it 3dB of gain on the fader, the crackle returned.
Here's the kicker. I was metering post-fader and peaks were still well below 0dbFS on the channel fader and the master fader.
I did some a/b listening with making up the volume on my CR monitors and with the un-gained audio, it was clean even with the monitors cranked.

I was clocking to internal, but also tried an external wordclock. I listened to both the analog outputs on my 96io and digital optical output via my Central Station's digital converters. Same results with all those variables changed.

i'm baffled. I've never heard or noticed anything like this before

I can post snippets if anybody wants to have a listen.
Any suggestions?

Greg

OS 10.4(something)
PT 6.9.3
G4 933

[InjuredEar]

Nobody else has encountered this?
Oh well. A colleague suggested that this may be a DC offset problem geting exacerbated by adding gain.


G

[Giles Reaves]

Nobody else has encountered this?
Oh well. A colleague suggested that this may be a DC offset problem geting exacerbated by adding gain.


G

Well, that's pretty easy to check - insert a High Pass filter into the chain BEFORE increasing the gain. Or use the output gain on the filter if it's available. The filter need not be set very high, you're cutting DC which is 0Hz!

Keep in mind that you may be clipping the D/A with reconstruction overloads (sometimes called "inter-sample-peaks). I'm no expert on this, but awareness is the key - knowing it CAN happen helps eleminate the possibility of creating them. In fact, the filter I recommended can create this problem as well! (nothings for free, even in the digital world!)

Good metering is essential for this kind of work. Spectra-Foo and InspecterXL are both good for this (I use InspectorXL). Only one plugin I know of actually has Recon Meters, the Sony Limiter (an excellent limiter, btw). I'm expecting more mastering plugins will have this important feature in the future.

Hope this helps...

[InjuredEar]

Can you elaborate on these "reconstruction overloads"?

[InjuredEar]

BTW, I tried the high pass filter thing and there was no improvement.

[Giles Reaves]

Here's some further reading about inter-sample peaks...

http://www.audioholics.com/techtips/...alplayback.php
http://www.prosoundnews.com/stories/...y/0724.4.shtml
http://www.record-producer.com/learn.cfm?a=2963

Sorry to hear the high-pass filter didn't help. Not sure this will either. If you can post a short example I could try to recreate the problem. I'm not sure how else to help, but this issue sure has me curious. ;-)