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RE: -60dB

It looks like you posted in the wrong place.

I agree that it's unlikely that Abe Collin's FFT averages over 60 seconds. Possible, but not likely. I know that my FFT averages over 65K points with my usual settings and this corresponds to about 2/3 of a second at 96 kHz. The points in the window are weighed with the central points counting more according to a formula that smooths out the plot. I generally use a Blackman-Harris window.

There are a lot of other issues involved with interpreting FFT plots, such as "FFT gain" which is a measure of how the noise floor varies in FFT plots according to the window size and window type. If Abe wanted to, he could calibrate his FFT gain by creating a test file with a 28 kHz tone and adjust the level of this tone to where the FFT shows it at the point on the suspect download file. A little knowledge can be a dangerous thing, but I'm confident that Abe Collins knows enough to figure these things out, if he hasn't already done so.

BTW, I have other software that I use that uses 8 million points. I've used this to do convolution by transferring to the frequency domain and multiplying. In addition, my player routinely does convolution at 2.8 MHz sampling rate with a time period of about 1 second (over 2,000,000 samples). I presume the software uses FFTs, to avoid the necessity of more than 10^14 multiplications per second using a simple time domain approach, which even if my hardware could do would run up a huge electric bill.


Tony Lauck

"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar



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  • RE: -60dB - Tony Lauck 07/12/1419:07:47 07/12/14 (0)

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