Play time

Finally, after quite a break, I have been playing with my 2 input, 8 output box again.

Interesting times. ADAU1452 still works as expected with EEPROM writing/booting fine, I left it at this point before moving last year.

Running the XLR inputs through ADC, DSP, DAC straight to 2 of the outputs works ok. I have played with it hooked up to my Cyrus One and CM10's. With this in the signal chain, or removed, I could not hear any difference. This was driven from my Asus Xonar U7 USB sound card which is pretty good.

Playing a bit more;  sometimes on power up, or using the reset button on the DSP board, there is a lot of static/hiss on the outputs. It seems to be coming from the ADC as unplugging the I2S cable removes the noise. Music still sounds fine, so unsure what is the problem. 

The PCM4202 board has it's own reset circuit, but is not reset from the DSP when this resets. Might trying enabling this with some tacked on wire. 

Had a quick play with ARTA demo. I am using my Xonar U7 for measurements for now. 

I am seeing low level 50Hz noise. This is an artefact of my setup. Even with the DSP box switched off (i.e. doing nothing) similar 50Hz is present (maybe 3dB to 5dB lower). On my Cyrus One, which is a sensitive amp (37dB gain), with the volume at max, I could hardly hear any low level hum. 

I have run some basic THD tests with around 1Vrms on the outputs (max the Xonar U7 line input can take). However these are not accounting for the U7's distortion, although that should be low (not sure at max input level though).
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20kHz = 0.046% (THD+N)
10kHz = 0.057%
5kHz = 0.045%
1kHz = 0.031%
500Hz = 0.030%
100Hz = 0.029%

I am happy with these for now. There are several issues to resolve, such as why the ADAU1966 reference voltage was low when last measured. All inputs and outputs are single ended, the XLR input negative terminal connects to ground at the Xonar U7 single ended output (which I am lead to believe is the correct way to do it). I also have no idea what I am doing with ARTA as I have not used it before, so this was just a quick play. 

Oh and I also have a 600Hz and 700Hz test signal on two of the other outputs, generated by the DSP, at around 1.7Vrms. Not sure if crosstalk from these has any affect yet. 

Example measurement below: