Earlier today I was abusing my Chaintech AV710, using it as a signal generator (coupled with a simple program) to test some hardware that I am busy building. Plugging the card's outputs into an oscilliscope (a cheap but respectable 20MHz analog model) I noticed several things about the AV710's analog output.
1) It clips under Linux. (I am using kernel 2.6.11 and alsa 1.0.8). There are two sliders in the ALSA mixer panel which change the volume - one labled Master and the other labled PCM. When the PCM slider is over about 70% of full scale, the soundcard output clips hard - even if the master is all the way down. Which means that you can get the card to produce nice square waves at even very low volumes. Fortunately with the PCM slider at less that 70% you can move Master up as high as you like and the output stays clean. The limit of clean output is around 400mV full scale.
I tried under Windows (Win2k with the VIA reference drivers) and couldn't replicate this phenomenon. With all sliders on max, the card outputs around 300mV, completely clean. The obvious workaround for Linux users is to keep the PCM slider at less than 70% of full scale. I have only noticed this on the front channel DAC - I can't get the high rate DAC to work under linux currently.
2) The Hi-Rate mode is fairly good Not only does the hi rate mode on this card sound good (due probably to the quality DAC, not the high rate) but it makes a very competent signal generator up to about 32kHz. At 30kHz, THD was still acceptably low however at 40kHz the signal was seriously amplitude modulated (with a 10kHz tone). Considering none of use can hear at 40kHz, this isn't a problem, unless you are a bat.
Full Version: AV710 Clipping Behaviour
I noticed similar problem on my laptop with onboard sound:
I made no measurements, but the sound becomes obviously distorted at about 70% of max PCM volume too. There is no such problem with fullscale Master volume.
Maybe the drivers ignore some hardware limitations ? (just a random guess)
CODE
vaio-z1 ~ # lspci | grep audio
0000:00:1f.5 Multimedia audio controller: Intel Corp. 82801DB/DBL/DBM (ICH4/ICH4-L/ICH4-M) AC'97 Audio Controller (rev 03)
0000:00:1f.5 Multimedia audio controller: Intel Corp. 82801DB/DBL/DBM (ICH4/ICH4-L/ICH4-M) AC'97 Audio Controller (rev 03)
I made no measurements, but the sound becomes obviously distorted at about 70% of max PCM volume too. There is no such problem with fullscale Master volume.
Maybe the drivers ignore some hardware limitations ? (just a random guess)
QUOTE (NumLOCK @ Mar 31 2005, 04:52 AM)
I noticed similar problem on my laptop with onboard sound:
I made no measurements, but the sound becomes obviously distorted at about 70% of max PCM volume too. There is no such problem with fullscale Master volume. Maybe the drivers ignore some hardware limitations ? (just a random guess)
CODE
vaio-z1 ~ # lspci | grep audio
0000:00:1f.5 Multimedia audio controller: Intel Corp. 82801DB/DBL/DBM (ICH4/ICH4-L/ICH4-M) AC'97 Audio Controller (rev 03)
0000:00:1f.5 Multimedia audio controller: Intel Corp. 82801DB/DBL/DBM (ICH4/ICH4-L/ICH4-M) AC'97 Audio Controller (rev 03)
I made no measurements, but the sound becomes obviously distorted at about 70% of max PCM volume too. There is no such problem with fullscale Master volume. Maybe the drivers ignore some hardware limitations ? (just a random guess)
If this is also the case with a completely different controller, it sounds like an ALSA bug. Anybody else got a different card and can test it under Linux? With a little more data I am sure the bug report would be more usefull to the ALSA guys.
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