What I was looking for is the "grass" that is present in-band and also out-band, past the 20kHz mark.
For PCM61 the higest off-band alias apears at -84dB, for TDA1541 at -70dB (worse), for PCM1791 at some -110dB (best).
In-band I have some "grass" between the spectrum at noise floor level.
You have two huge off-band spikes mirrored around the 22.05kHz and you have a lot of in-band "grass" that rises numerous times to -80dB (don't know what the averaged total would end up). That is distortion of the original signal.
Now... What I don't know is why you don't have any beats between the fundamentals in your signal. What ADC are you using?
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I redid my measurements with different setup for the ballanced inputs (to accept unballanced signal). No change.
Loopback E-MU1820m, PCM61@0dB, PCM61@-60dB, PCM61@19+20kHz@-3dB. I still don't get what's up with the beats...
Loopback E-MU1820m, PCM61@0dB, PCM61@-60dB, PCM61@19+20kHz@-3dB. I still don't get what's up with the beats...
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Hi,
In the signal. Generate a test signal, for example using Audacity etc...
Ciao T
In the signal. Generate a test signal, for example using Audacity etc...
Ciao T
For -60 dB, did you adjust the MSB ?
You can do it using a headphone, adjusting for most pure tone
and watching the live measurement, grass sinking in the noise floor.
Also try other pcm61 chips, you may find better ones.
I did ajust the MSB, it did affect the 2nd harmonic the most. Maybe I can redo the adjustment now, with the better card.
I have (6) PCM61 but didn't really had time to rotate them. I was thinking to parallel them when I am bored 🙂
I have (6) PCM61 but didn't really had time to rotate them. I was thinking to parallel them when I am bored 🙂
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