Digital Volume Control - Best Practice

[Nor]

Hi


I have VortexBox Appliance (more than great!!), and I'd like to try this technique,


does anybody know DD converter which can handle 24bit (with USB) working on linux?


Not so expensive... I already have stand-alone DACs, so I prefer DDC.


In my understanding, M2Tech HiFace doesn't support linux now.


Turtle Beach Audio Advantage Micro doesn't support 24bit with USB (Am I wrong?).


Or another way to do this?




Thanks in advance.

[sonorejr]

Nor, take a look around in this website for possible digital converters:


http://www.alsa-project.org/ma.....atrix:Main


It's not a definitive list as I know other units work, but it's a start….


I would pass on the turtle beach and not much info on it on their site. The http://www.sonore.us

[jegunn]

I have a couple of (probably uninformed) questions about this. Why do you need to specify a sample-rate converter? Is the idea not just to extend the
word length so that when you multiply/shift to change the volume the low-order bits are not lost? Or is this just some MPD artifact that it
will not actually DO this unless you invoke some floating-point conversion like a sample-rate converter?

Second, is there any test to make sure it is working properly? It *seems* to work, but the /proc/asound/card0/mixer file says

Card: Bladelius Bladelius USB Audio 2.0 at usb-0000:00:1d.7-7, high speed
Unit: 10
Control: name="Bladelius Clock Selector Playback Volume", index=1
Info: id=10, control=2, cmask=0x0, channels=1, type="S16"
Volume: min=-32512, max=0, dBmin=-12700, dBmax=0

Which is not reassuring that it is dealing with 24 bits; on the other hand, the stream0 file says the data format is S32_LE,
which sounds right.

BTW, the Bladelius USB DAC is *WONDERFUL*. Asynchronous, isolated, minimum-phase filter, 24/192, musical, accurate. I
cannot tell the difference between it and the Ayre QB9 at 4 times the price, and they are both head and shoulders
above any other DAC I have ever heard. And it works perfectly with MPD/VortexBox Player.

[sonorejr]

jegunn, at this point I'm not sure we should be using this procedure. It was theoretical and should have worked, but was not tested. Also, a lot has changed about the way mpd works.

FYI the USB 2.0 (AKA high speed) dads and interfaces use the S32_LE format by default so mpd will convert to this format automatically. No need to worry as this format change will not affect bit perfect playback.

Thanks for the info on the Bladelius USB DAC.

Jesus R