A how to for a PC XO.

[StigErik]

There's no processing going on in the soundcard, just AD and DA conversion, and software-based DSP wont change that. A few cards also have additional functions like digital volume control, digital mixer or even sample rate conversion, but no soundcards I know have any advanced DSP functions.

You nailed it - DRC is best applied below the Schröder frequency, usually ~200 Hz.

[otto88]

Thanks Stig

If the soundcard does not do digital volume control (DVC), I’ll check if Allocator does.

I’d been tossing up doing the Lightspeed Attenuator or a variant, but DVC sounds a lot simpler . . if there is no trade-off . .

[StigErik]

You can do volume control inside Bidule, but its cumbersome....

I chose to do volume control at the source - I use a Squeezebox, it has a 24-bit digital volume control with 0.5 dB steps. You wont loose any resolution until you are at -35 dB or so. Nothing to worry about.

[tritosine]

Theres trade off , you need DA converters with ~ 128SNR. ES9008, PCM1798, 94, and sub 50ps jitter. >21 bit perfomance.

[tritosine]

BTW attenuator with cmos switches or r2r dac is so simple and neat.

[StigErik]

Why 128 SNR? In a real-life situation, you wont get more than 90 dB SNR anyhow, limited by the background noise in your room and the max SPL of your speakers.

Everything has tradeoffs. You will loose resolution with an analog attenuator as well, as the signal will in the end disappear into the noisefloor....

[tritosine]

A commercial DAC thats not accurate (most) , sinks into nonlinearity very fast adds various harmonics and stuff . Surely not analogue tape alike nonlinearity or noise.

With CD's the dither is not straight line white noise but shaped, it reaches even -70, -80 around 20khz, but below that, in the critical freq's it s actually below -120 dB!

When they add the tracks together in the mixer, those tracks are still 32bit, and right until the final dithering theres information there, especially if it was attenuated during mixing. So for at least 15 years now all plain, professionally mastered cd's can contain useful information up to 20th LSB. I'd better listen to those come out in a linear way.

[StigErik]

Maybe there is information on our CD's at -120 dB, but how do you expect to hear it? Even if you had a totally quiet room you would have to play it back at 120 dB or more peak level. In a typical home situation, the background noise is at least 30 dB, masking everything below -80 dB anyhow.....

[tritosine]

Im not expecting to hear it,right now Im dropping 36dB out of this es9008, for music to be like "background" noise, but I still have 16.5 bit linear headroom, because the chip has 134dB to start with.

[StigErik]

Originally Posted by tritosine

A commercial DAC thats not accurate (most) , sinks into nonlinearity very fast adds various harmonics and stuff . Surely not analogue tape alike nonlinearity or noise.

Yes, a good reason to ensure you have properly set analog levels when doing digital volume control. You should approach 0 dBFS at your preferred listening level. I have an 8-channel dac with adjustable analog levels. I have set those so the digital levels are as close to 0 dBFS as possible.