Player decoding or Receiver decoding, that is the question

[EWL5]

Originally Posted by welwynnick

I don't know what's different about this forum, but many people seem to take their opinons from those who claim to know what they're talking about, rather than being a bit more scientific (which I am!) and learning and understanding things for themselves. Unfortunately this is a complicated question that I've been endeavouring to unravel for a year or two, and I've only made some practical progress in the last few days. I've been reporting things on a day-by-day basis elsewhere, so there's a documented record, and this is quite pertinent.

Firstly, there's no reason why bitstream should sound the same as LPCM. The digital audio replay architecture is different, and that means the sound may be different. I'd better explain that, quick.

A digital audio signal has two elements - a data stream and a timing stream. Both of these end up at the DAC to create the analogue audio signal, and both need robustness and fidelity.

These streams are quite distinct, and take different critical paths:
The data stream starts at the disc, and ends up at the DAC.
The timing stream starts at the master clock, and also ends up at the DAC.

The bitstream decoding process only affects the data stream, and I think we are all pretty confident that that is lossless, so the DAC is receiving the right data, whichever decoding architecture is used.

However, this architecture MAY affect the path of the timing stream . This isn't necessarily the case, but my experience with the Onkyo suggests that it is. With LPCM, the clock is in the transport, and the path takes the HDMI connection to the receiver and too the DACs. This is a tortuous path, and is full of degradation - like toslink but worse. With bitstream, there's no clock associated with the data because its compressed, and the clock is regenerated in the amplifier, just as it is with DD and DTS. This places the clock right next to the DAC, with robust and direct connection, which is ideal. This doesn't eliminate interference, noise and jitter, but its a very big help.

So with bitstream there is an opportunity to minimise jitter, though this is only achieved if the amplifier doesn't generate its audio clock from the players video clock, in the same way it does with LPCM. For ayear, I've never known which it was, but I think that question has now been answered in my mind, now. Of course, my observations may not apply to other amplifiers, like Pioneers, which have different architectures. I'm itching to find out....

Nick

I'd love to do a double blind jitter test with you. I haven't met a person who claims to hear jitter during multichannel movie soundtracks. With the dynamics involved, it's almost pointless (perhaps a different story for high resolution stereo music).