Topic: HDSP 9632 with AO4S-192 - Phase cancellation problem
I sent an email to the general tech support address, but I thought I'd post this here in case the solution is helpful to others.
I'm running a 5.1 surround production setup using the HDSP 9632 and the AO4S-192 expansion board, and I'm experiencing a phase cancellation problem. I'm feeding all 6 analogue channels into my sub (JBL LSR 4312SP), the sub is performing bass management on those 6 channels, and then the non-bass signals are passed to my L/R/C/LS/RS monitors (all are JBL LSR 4326).
What appears to be happening is that AnalogueOuts 1/2 (balanced breakout cable) are out of phase (phase inverted) with AnalogueOuts 3/4/5/6 (AO4S-192 expansion board). If I send the same stereo signal through all 3 stereo pairs, I get a dramatic reduction in bass once the same signal is active on AnalogueOut 1/2. Whereas, if I have only have the signal going through Outs 3/4 and then send the same signal through 5/6, I get an appropriate boost in the bass signal produced by the sub. If I delay AnalogueOuts 1/2 by 100ms or so, or phase invert that channel, the bass behaves as expected (I get a bass boost), so that's why I think there's phase cancellation occurring.
I'm pretty confident that the sub, breakout cable and balanced cables are not the problem. Specifically, the sub doesn't sum AnalogueOuts 3/4/5/6 in way that cancels the bass. I also changed the XLR cables connecting Outs 1/2 to the sub (same problem occurs). Furthermore, I switched to the non-balanced breakout cable for Outs 1/2 and saw the same problem.
To rule out my software as the cause, I used Cubase 5 and I also used a 5.1 game audio engine called FMOD to produce the signal. Both yielded the same results.
Is it possible that some setting for my RME cards is causing a phase problem between the HDSP 9632 and the AO4S-192 expansion board? I should mention that if I route all 3 signal pairs (via the totalmix matrix) to AnalogueOuts 1/2, the summing seems to be fine (i.e. no phase problems occur at this point in the signal routing), so the problem would seem to be further down the chain.
Some basics about my system:
8 Gigs of RAM
Intel i5 750 2.66 GHz
nVidia GTS 250
UAD-2 Quad Core PCIe card
Let me know if you need any further info.