I was looking for a cheap but high-performance solution for an entry level integrated amplifier. Many entry-level amplifiers these days have a built-in DAC with SPDIF input (COAX and/or Toslink). So, I ordered Amazon Basic Audio Extractor reading this review. I thought Raspberry Pi HDMI output to SPDIF input of such amps via the Audio Extractor might be the best and most inexpensive (cheaper than I2S DAC or DDC HAT for Raspberry Pi) music player solution for an entry level integrated amplifier.
However, it did not work for my integrated amp DENON PMA-800NE. I measured THD+N from the pre-out of the amp with Cosmos APU/ADC and REW.
Raspberry Pi I2S -> HiFiBerry Digi+ Pro COAX -> PMA-800NE COAX: THD+N = -90.8dB
Raspberry Pi HDMI -> Amazon Audio Extractor COAX -> PMA-800NE COAX: THD+N = -82.7dB.
Comparing them, THDs are almost same, but noise level is much higher with the Audio Extractor.
View attachment 249432
Then, I connected to COAX output form the Audio Extractor to TOPPING D50. Surprisingly, the results were almost same, even with the Audio Extractor was slightly better! Also, these results are almos same as the measuremnet of
TOPPING D50 USB input by Amir with AP.
View attachment 249433
I have Marantz NR1200 too which has HDMI input as well as SPDIF input. As you see, HiFiBerry Digi+ Pro and direct HDMI connection from Raspberry Pi to NR1200 are almost same (THD+N = -103dB). But With the Audio Extractor is very bad (-85.dB).
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I cannot explain the reason of the results as the digital output from the Audio Extractor should be exactly same. The only explanation I can find is that the Audio Extractor have much jitter and TOPPING D50 can handle them well (with enough buffer?) but PMA-800NE and NR1200 cannot do that. What do you think? Any thoughts?
Following table is the summary of each THD+N.
View attachment 249447
PS: I used IEC958_SUBFRAME_LE ALSA driver (and ‘hdmi’ card to covert PCM to IEC958) for this test. I double checked with the Mac HDMI output, CoreAudio Exclusive Mode and REW Signal Generator. However, results of the two machines and drivers were same.