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
