USB audio poor quality...

[jacum]

Hi to all.

I use a USB D/A converter and a SCYTHE SDA-1100 Class D amplifier connected to a pair of Cambridge Audio bookshelf speakers.

I recently noticed (rebooting into linux after a long time) that the sound quality in linux (same computer, same external audio equipment, obviously) is much better.

I was wondering whether I have to play with some sysctls in order to reach a good quality in FreeBSD, just like it is in Linux.

The first aspect that showed up is the much lower output level in freebsd FreeBSD, that compels me to increase the volume on the amplifier very much in comparison to what I need in linux.
Maybe this also affects the poor audio quality when it comes to a lower level in the amplifier inputs.

If anyone knows, please give me some hints in order to tune the driver (sound(4)) so that the quality may be improved.

Thanks in advance for any help.

FreeBSD-9.1 RELEASE.

Giacomo Strangolino.
Elettra - Synchrotron Radiation Facility.

Italy

 

[xa]

When switching from integrated sound system to external USB DAC i'm following next steps:

1) Add to /boot/loader.conf (example for 44.1/16bit stream, of course)

hw.usb.uaudio.default_bits=16
hw.usb.uaudio.default_rate=44100

And in console (if pcm.2 - is your USB audio device)

sysctl dev.pcm.2.play.vchans=0
sysctl dev.pcm.2.bitperfect=1
sysctl hw.snd.default_unit=2
mixer vol 100:100
mixer pcm 100:100

<- this enables bitperfect and also disable vchans, so the first application which captures the audio output will be "unique" playing sound. After that software volume mixer don't works (because "bitperfect") and i change volume on my external amplifier.

Sound quality is brilliant

 

[jacum]

Hi Xa,thank you for your reply.

I already tried with

vchan=0

and bitperfect.

Apart, as you said, that with bitperfect much of the sound system stopped working,
I did not notice any significant improvement in the audio quality (especially if compared
with the extreme difference which is evident using Linux).

I will try with the bits and bitrate settings, although I think that, being the DAC correctly recognized as 16/44100, the driver is already correctly setup. Or do you think not?

Anyway, I will let you know!

Thanks again!

Giacomo.