Qball's Weblog

Quality of soundcards

Tags mpd  Music 

I often make the remark that soundcards in laptops/motherboards are bad.

F.e. I say “It does not perform better then 12 bit”.

What I mean by this is the following:

If you turn an analog signal into a digital signal, you introduce errors, because you only have X defined levels, not infite as with analog.

So the more bits you have, the more levels you have, the less noise you introduce. The error that you make is 1/2 an LSB (least significant bit).  Any noise in the system larger then this 1/2 LSB can cause that the outputted value does not represent your input value.

This gives you a maximum noise your system may have if you want to output X bit signal. (It must be smaller then 1/2 a step, so in 8bit (256 levels) your noise should be lower then 1/512 of the maximum value)

So if your soundcard has a -80dB SNR (signal to noise) you can calculate  how many bits this can maximal represent, any more bits will be “lost” in the noise.

A rule of thumb is: ENOB = (SNR(dB) – 1.76)/6.02 (f.e. see Intergrated converters by Paul G.A. Jespers).

So if you have the 80dB SNR you can represent an ENOB(exact number of bits) of almost 13 bits.  Any more bits, are smaller then the noise and cannot be represented.

If you look at a common onboard soundcard spec, you get an SNR of the 86db, so 14 bit. But this is static, your dynamic performance is often even worse.

For example the realtek ALC850 Chip (used on older asus motherboards) has an SNR of 86dB, 14 bit. But it dynamic performance is 70dB, that is only 11bit! In real life it might be even worse, because noise from your PSU is also added, this realtek supresses the noise by only 40dB.

To compare, to correctly represent a CD you need 98dB SNR static and dynamic.

This, in short and with some simplifications, is why most onboard soundcards suck.

So if your resampler makes -80dB noise, with this soundcard, you hardly need to care about it.


p.s. To get the more correct full picture, I advice you to get a good book on ADDA converters. like the one by Jespers.