This "feature" isn't a feature, or a bug - its how optical out works. With any device. When I have my DVD player or my XBOX plugged into optical out, the volume control is done on the receiver. This is because the output device is sending the raw digital data.

I didn't mean to imply that the hint was bad though - being able to adjust the volume level of digital out from the computer is pretty useful, though you may lose some audio quality this way, so audiophiles beware.

"This "feature" is both annoying and unneeded."

This feature is intentional and appropriate when using digital outputs. The audio stream should be clean and true to the original audio when transferred to your receiver. This is the whole intent of using digital audio cables. Adjusting the volume digitally modifies the audio data, and if you increase the volume over the base level, it will cause clipping. Fixed outputs also keep all of your digital inputs and fixed level line inputs at roughly the same volume level (assuming the source material is reasonable).

There are times when being able to adjust the source volume may be helpful, but saying fixed level digital output is unneeded is not true. For the best quality, if you don't need it, leave it as it is.

Enquiring minds want to know how adjusting signal strength on a digital receiver is good, but adjusting signal strength on a digital broadcaster is bad.

It's digital folks. Adjusting the volume is simply nothing more than applying a mathematical modifier to the equation describing the data. No data is destroyed, no clipping occurs. If you get distortion its because of analog line noise in the cables, speakers, etc.

Adjusting volume at the digital signal stage requires re-computing the sample values, and results in loss of resolution and/or clipping of the waveform.

Your receiver is adjusting volume by controlling the gain of the amplifier stage -- the signal isn't adjusted digitally.

That doesn't make any sense. Digital is digital. You don't need to resample the bits, you just need to apply a modifier to the waveform equation multiplying sinx by 2 doesn't distort the sin wave. Time to do some research, I guess.

I found the answer from a link another commenter sent me. The signal is not distorted as long as your gain is done in steps that don't result in rounding errors. So it is possible to adjust volume on a digital signal without creating distortion, just not trivial.

Agreed. Its not a bug.

"assuming the source material is reasonable"

Not all sources are reasonable. And sometimes you want to be able to use your little Front Row remote that's in your hand, instead of fumbling for the receiver remote.

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No this feature is not unneeded, digital volume setting screws up the audio quality.

Feel free to explain how adjusting the volume of a digital signal reduces its quality. It's digital. 10110101101 at 3 volts and 10110101101 at 6 volts are identical.

Thanks. What that tells me is as long as you step your gain in multiples that do not introduce rounding errors, you will see no distortion.

So the more accurate statement is that adjusting the volume on digital audio MAY cause distortion if it is done poorly.

No, the audio data will always be altered by the scaling operation (which amplification/deamplification in the digital domain really is all about). There are techniques, however, as the linked article suggests, to apply dithering to partly hide the effects of the scaling.
To explain this further, assume you have audio data in 8-bit which utilizes all the dynamics available in 8-bit. Then you have samples ranging from all ones (255) to all zeros. If you apply half volume on it, the resulting audio data would be scaled to range from 127 to 0, as if you would have removed (actually truncated) the last bit on the original audio. Two samples in the original stream that had the values say 127 (0111 1111) and 126 (0111 1110) would now have scaled down to 63 (0011 1111) and 63 (0011 1111) - that is they are indistinguishable and thus we have lost information in the process.
Dithering is a technique to overcome this. A simple kind of dithering would be the following:
Say we had two consequtive samples in the original audio data with values 127 and 127 (see bit patterns above). The scaled samples should have been 63.5 and 63.5, but this is impossible. The idea of dithering is to compensate for this by making the first value 64 and the second 63, which evens out to 63.5 and to some extent more preserves the characteristics of the original data.
But it is still not the same as the original data, right?

Oddly, you *can* adjust the volume of music played over an Airport Express even when it's using an optical cable. The volume slider in iTunes still functions normally. I assume some sort of dynamic digital de-amplification takes care of this, although I can't say I really notice a drop in sound quality when I turn it down.

However, lowering the volume from max does prevent multi-channel audio from playing correctly. I tried a DTS-encoded WAV file and it plays correctly on full volume but turns to static at anything less than 100%.

I'd be very surprised if this doesn't screw up AC-3 and DTS pass-through in DVD player (or VLC or Perian or any other apps that can do it). At best, you'll have to have the volume maximized to get it to work. The passthrough ability is one good reason to have the volume locked, because any alteration to one of those compressed formats is going to prevent the receiver from decoding it.

"I'd be very surprised if this doesn't screw up AC-3 and DTS pass-through in DVD player (or VLC or Perian or any other apps that can do it). At best, you'll have to have the volume maximized to get it to work. The passthrough ability is one good reason to have the volume locked, because any alteration to one of those compressed formats is going to prevent the receiver from decoding it."

Using this method you have to change back to digital audio for watching anything that needs surround sound, something you can easily switch from within VLC.

I wrote this guide because for some reason you can easily change the volume settings within Vista and the inability to do it within OSX made me angry. Yes I know why the volume is locked to begin with, it is raw data, however my ears can't tell the difference when I am just surfing the net while listening to music on iTunes which can adjust volume itself.

This guide isn't for the audiophile, it's for the average joe who likes to use their apple remote or volume keys while listening to music over optical. When I load up a high definition movie I simply tell VLC to output to Built-in Output (encoded). In fact I think I can make it do that all the time in the settings.

Not to mention I HATE my remote for my receiver, it is complete garbage.

And yet, even more interesting is the fact that the keyboard volume softkeys work under bootcamp when in optical out mode.

To me its an inconvenience, given that the control module for my Logitech Z-5500 is out of sight and I have to reach behind the iMac to adjust the volume. The reason I use the optical out is to bypass the NASTY headphone port noise!!! I use the headphone port on the Logitech's module instead.

I bet there is a defaults.write setting somewhere that can enable it via the terminal.

Alternatively, I plan of getting a Firewire or USB audio interface, the onboard audio SUCKS! I didn't expect this in a $1800 machine!!!!!