Subject: Re: getting a signal level from a signal+noise measure? From: Eric Delory <eric.delory(at)UPC.ES> Date: Sat, 11 Sep 2004 18:55:24 +0200Hi Rochelle and all, First you must go back to linear domain, forget the glossy dB domain for a second. Under the hypothesis that your signal and noise are uncorrelated - hopefully that is true, the estimated absolute received power is the sum of the speech signal and noise variances. This comes from the mathematical expectation of the cross-correlation of speech and noise being zero. So you end up with: A^2 + B^2 = C^2 where A is the noise standard deviation (square root of the variance), B is your speech rms amplitude, and C the resulting signal rms amplitude. Knowing C and A, you have a relatively good estimate of what B is. Now you have your speech amplitude in dBrms: from 20 log10(B/B0) where B0 is 20uPa or whatever reference you find appropriate. Hope this helps. Eric. Answering Rochelle Newman: -> I realize this would never be exact, but is there a formula for mathematically subtracting out the dB level of the noise level and then transforming this in such a way that one can get a rough estimate of the amplitude level of the signal alone? (Or, is there a mathematical function for dB that tells you what level A is at if you know A+B and B alone?) ______________________________________________________ Eric Delory Laboratori d'Aplicacions Bioacustiques D164, Escola Politécnica Superior d'Enginyeria de Vilanova i la Geltrú Universitat Politécnica de Catalunya Avda. Víctor Balaguer s/n 08800 Vilanova i la Geltrú Barcelona, España. Tel. (34) 93 896 72 27 Fax.(34) 93 896 77 00 H/P.(34) 655 33 0196 eric.delory(at)upc.es