12 Dec
2004
12 Dec
'04
2:04 p.m.
Probably, the last questions today :-)
1. What is the meaning of the "10 * log10 (Fsample / 2)" part?
2. When noise spectrum is approximately flat - is there
a common correlation with A-weighted value (say, "about 10db")?
Andrew
======= On Sunday 12 December 2004 17:05, Fons Adriaensen wrote: =======
On Sun, Dec 12, 2004 at 03:04:31PM +0300, Andrew Gaydenko wrote:
In othe words, a card SNR is blue, as our ears do not
integrate a
sound during such long period of time. But for more o less constant
noise spectrum (which is true for any card), noise integration alow
us to expand measurement range (about 20db in my case) - gray spectrum.
...
To measure the SNR of your card:
- Disconnect all input signals.
- Set the display range so you can see the noise. This spectrum
should be flat, except at the lowest frequencies.
- Switch on the VidAv function and put a noise marker in the
flat part of the spectrum.
- Read the noise density value, No, in the upper left corner.
Now compute -(No + 10 * log10 (Fsample / 2)), this is the SNR.
Example: you read No = -130 dB/Hz, and the sample frequency is
48 kHz. 10 * log10 (24 kHz) = 43.8 dBHz, so the SNR is
-(-130 + 43.8) = 86.2 dB.
This assumes the noise spectrum is flat. If it isn't you need to
integrate No over the frequency range. Future versions of JAAA will
probably contain a function to do this, together with A-weigthing.
--
FA