Volume control with digital output?

[Magnoliaq]

Hi all. Need your help with something that's been perplexing me for awhile.

I have my C-300 digital optical output connect to a stereo receiver. The digital coaxial connects to a separate multi-channel receiver.

I found that I can control volume using the C-300 remote control for the optical out (for stereo music purpose). The remote control has no effect on the digital coaxial out (for movie purpose).

I thought that generally you can't control volume if you use digital outputs, of any device, not just the C-300.

Not that I'm complaining or anything. I just want to understand what's going on. Anybody?

[halfelite]

your stereo music is an analog source so you can control the volume its just analog going over digital the pch is doing the decoding on the audio. Movies on the other hand I assume are things like DTS/DD they are a digital format and sent out bit by bit for your receiver to decode so the audio cant be touched in that case.

[plm]

In this case we're talking about digital signals from end to end. The reason it can't change the volume on multi-track audio is that it passes through the digital bitstream untouched. To alter the volume it would have to decode the multi-channel DD/DD+/TrueHD/DTS/DTS-HRA/DTS-MA (and the couple of others) stream, apply a digital gain adjustment to each channel of the resultant PCM audio and then re-encode it back into the same stream format to output. Even if it has the decoders for particular codecs (and it doesn't have all of them, for example TrueHD) it certainly doesn't have the encoders to be able to re-encode the modified stream.

There is a conceivable way to do this, which would be to output multi-channel PCM, but the Toslink interface doesn't have the bandwidth for that anyway, so it could only work over HDMI. And, even then, TrueHD would be out since it doesn't have a decoder.

The reason it works on stereo music is that it is PCM audio to start with and so it's easy to apply a gain adjustment as there is no decoding/re-encoding process to go through.