First test. This is really testing BOTH the D/A in my Yamaha I88X and the A/D in the PCM4222 evaluation board. The test setup was as follows:
- Nothing was calibrated.
- 16-bit 0dBFS-peak-amplitude sine wave .wav file (courtesy of RME Audio)
- D/A output is direct from a I88X output opamp (ie it has no volume pot or attenuator)It's rated at +18dBu max output level.
- A/D input is direct into the A/D opamp buffering stage(ie no preamp, amplification factor is -.482(-6.34dB), A/D is rated at +14.68dBu for 0dBFS)
- Unbalanced and crappy (less than optimal - lose 6dB) cable interconnect
- Recorded sample was normalized to 0dBFS (since the D/A and A/D have different reference levels).
- Recorded Sample was "time aligned" to original sample and then phase reversed (does not include all latencies involved)
So, you can see the test is pretty flawed to start with. I am really measuring both the A/D and D/A. When summed together the waveforms don't cancel out 100%. However, looking at the waveform on my audio editor (zoomed in at the sample level) they "look" almost identical. BTW, I tried clipping the A/D with the Yamaha and wasn't able under normal circumstances. The only way I could (and only barely) was driving it with the master outputs in the I88X, which do have an active output stage (volume control). I guess this is because of the 6dB drop from running unbalanced cables. The original file is named 0_16.wav
I'll make some other tests, including an actual music recording...