On 10/08/2015, Sampo Syreeni <de...@iki.fi> wrote: > > Do notice that we're in the business of producing audio systems and > software. Not all of them are meant for pure human consumption. For > example, in audio forensics work, you'd like your signal chain to be > pure enough to pick up line hum at -60dB or even -80dB below the already > low noise floor, given enough integration time.
Here is a little 'audio forensics' challenge for you. I created a -30 dB white noise signal: http://morpheus.spectralhead.com/wav/noise_30db.wav I created a mixture of two sine waves with amplitudes -90 dB and a -110 dB (which are -60 dB and -80 dB below the noise floor, as you suggested), using 32-bit precision processing. Then, I mixed these two sine waves with the original noise floor, resulting in this signal: http://morpheus.spectralhead.com/wav/noise_30_sine_90_110.wav My question to you: What are the frequencies of the two sine wave signals, that are -60 dB and -80 dB below this noise floor? To help you with your analysis, here is a 60 second long version in full 32-bit floating point precision [10 MB]: http://morpheus.spectralhead.com/wav/noise_30_sine_90_110_32bit.wav I believe you won't be able to tell, whatever you do, because the two sine waves are 1000x and 10,000x quieter than the noise floor (that is, 10-15 bits below the noise floor). In case you're wondering how the spectrum looks like, here's the analyzed spectrum of the full 60 second sample: http://morpheus.spectralhead.com/img/noise_30_sine_90_110_spectrum.png I marked the -90 dB and -110 dB levels with red lines, that's where you should be looking for if you want to find the two hidden sine waves. All you need to do is tell me the frequencies of the two sine waves. But my guess is that your audio forensics magic will fail you, and you won't succeed. But good luck trying. If you don't tell me the frequencies within one week, I'll assume you failed. -P _______________________________________________ music-dsp mailing list music-dsp@music.columbia.edu https://lists.columbia.edu/mailman/listinfo/music-dsp
