[linux-audio-user] A most bizarre problem.

A few weeks into my admittedly bizarre Jack-based telephone logging + music-on-hold system, I ran into an interesting "bug". But first, the hardware in play: Motherboard: ECS P4IBMS (Pentium 4, i845 chipset) 00:1f.5 Multimedia audio controller: Intel Corp. 82801BA/BAM AC'97 Audio Card: Intel 82801BA-ICH2 Chip: Realtek ALC200/200P rev 0 ALSA-1.0.3b w/1.0.4 drivers + libraries, jackd is from late April 2004 CVS. My jackd invocation line is as follows: jackd -R -d alsa -S -C -p 4096 -M -n 2 -r 11025 I have an AT&T MERLIN phone system in my closet along with my main home server (see above hardware description). I have my PCM (Line out) plugged into the MERLIN system's music-on-hold port, that works well. I have two phone lines hooked up to JD Audio Phone Patch boxes to provide local + remote side level correction (trans-hybrid technology), which feeds into my Line In jack [each patch box provides a mixed in/out audio source on a mono output, so I have Line 1 feeding Left, and Line 2 feeding Right]. This too works beautifully with my vox-activated audio logging program which I'd adapted from one of the jackd sample clients. [It's ended up quite something else, but not too bad if I say so myself.] PROBLEM: When I have someone on hold on Line 2, say, and someone else is talking on Line 1, the person on Line 2 hears the music-on-hold *AND* the conversation of Line 1!! It gets better. If I dial out on Line 3 [lines 3+4 are outbound only], put that call on hold, and there are people talking on Lines 1+2, the caller at the other side of Line 3 hears not only the music-on-hold, but BOTH Line 1 + 2's conversations!!! YIKES!!! This was a big shocker. Naturally, I never did this sort of testing, being more concerned with DC bias, filtering curves and bandpass settings, and which compressors to use for the online-browsable phonelogs as well as the losslessly-compressed (FLAC of course) data archival logs. Obviously the PCM output is being mixed into whatever feeds into the Line input of the AC97 codec. This is annoying, and I can see no way of switching it off. I've explored every Mute/on/off option in the alsamixer, alas the dark fire did not avail me. I see nothing about "hardware monitoring" as an option for this chipset, however Hammerfall and others are mentioned as supporting this feature; nothing in the intel-8x0 driver suggest this is a supported feature. I'm relatively new to PC audio hardware, but has the LINE-IN been fed into the PCM output mixer from the beginning? Is this a funky chipset bug or weird issue or interaction? I know that the output mixer is fed audio from the CD and the WAVE device, but it seems a bit strange that the LINE-IN port is also routed through in this way. I can't try this under Windows, as this machine has been kept clean from the Dark Software of Udûn since its deployment. I obviously can't mute the PCM output, since that's the music-on-hold. After much experimentation, I figured I'd try the Microphone input instead. It seems noisier, even with the +20dB turned off. The impedance is quite a bit different, though fortunately I can get by with the gain set to the bare minimum [3 in the ALSA mixer, which is the smallest non-zero value I'm allowed]. But the cross-surveillance bonus to the music-on-hold problem is gone. Maybe I can do something tricksy like emit the music-on-hold on the right channel only, and hook up Line 2's audio feed into the left channel of the LINE-IN. This is a cruel hack which depends on the mic+mix functions in the codec doing their job properly, which is a huge ask. Ah well. I'm back in action, only now I have only one channel of recording capability. :( :( Is there a mixer option/setting to disable this "pass-through" routing of LINE-IN to the LINE-OUT sound port? In Mordor where the PC platform lies, =MB= -- A focus on Quality.