S/PDIF is here to stay

With playback working again it was time for another addition; digital out. After some soldering and enabling I2S on the decoder the setup was ready for test run. Hooked the monster up to an Onkyo receiver and voila.

First some details. Currently the VS1053B is configured to output a samplerate of 48 kHz (this is also the highest supported samplerate for all codecs). This goes directly into a CS8406 S/PDIF transmitter which is wired in hardware mode. A second option would be a 96 kHz I2S signal. Even though the decoder support 192 kHz it can only output it with MCLK divided by 2. The CS8406 only supports clock ratios down to 128 * Fs. For 192 kHz to work it must go down to 64 * Fs.

At the moment it only uses TOSLINK, but the final version will also have coaxial output. It’s just that I don’t have the required pulse transformer lying around.

Back to the receiver. It detects the output as a 44,1 kHz PCM signal. For a more isolated test I hooked up AKG K 701 headphones which is know for it reference like quality. And wow, what a thrill. This was simply the best sounding audio I’ve ever heard not coming from a real CD.

I could still hear some things I didn’t like (high tones), but at this time it’s unknown what the cause is. Could be the recording itself (need to compare with original CD), it could be samplerate conversion (48 kHz to 44,1 kHz), could be the setup (just think of how anal audiophiles can be about the smallest things ;)), etc. Just a matter of proper testing, listening and comparing.

Also one thing that’s bothering me is the interference the setup has on my cable TV signal (doesn’t affect HDMI). At the moment I’m just blaming all the breadboard wiring which probably acts like a small transmitter. The board is located almost directly below the inputs of the TV and since the cable signal already is very weak (some stations are half snow even without any other electronics close by), so it’s not directly a problem (not to mention the lack of programmes worth watching… but that’s another story ;))

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