- Thread Starter
- #21
Quick follow-up on this one. For all the below FFTs, I measured WAV files directly, not through a device. I created the WAV files with Audacity or REW.(...)
Now, can we actually do better than that still...? Yes, yes we can - the 999.91 Hz he suggested gives basically perfect-sounding white noise. So we want a prime multiple of a small fraction of 1 Hz, eh? In this case, that's 0.01 Hz, meaning a 100 second interval.
I had an algorithm search for all primes between 999999900 and 1000000099 and got lucky, it found 9.
(...)Code:999999929, 999999937, 1000000007, 1000000009, 1000000021, 1000000033, 1000000087, 1000000093, 1000000097
I created two test tones with REW, without dither. The first one at 997Hz and @-0.01dBFS:
The second one at 999.91Hz and @-0.01dBFS:
And you were right, the 999.91Hz is self dither, which is very interesting for our purpose of testing devices.
Now, here below is a 997Hz with rectangular dither (from Audacity):
We lose 3dB of resolution due to the dither.
And the same 997Hz @-0.01dBFS from REW instead of Audacity (with dither again):
You can see that the noise floor raised again by 1.7dB because of the different dither from REW.
Last and not least, this is the view of a 1kHz @-0.01dBFS without dither:
As you said previously, we see a nice slew of 100 Hz harmonics, which reduces the THD measurement by 22dB compared to 999,91Hz!
Conclusion
I think the 999.91Hz is a really nice choice. No need to dither and so we save 3dB of Noise when compared to Rectangular dither from Audacity. It means that straight from the -0.01dBFS tone, we can get a reliable measurement of SNR (although it should be measured with -60dBFS test tone as per the AES). We also get 5dB more for THD measurement, in case a DAC would be good enough to go below -130dB THD
I suppose we have a winner for the new pseudo 1kHz measurement.
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