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centerchannel68 · Jan 22, 2007, 11:32 PM

What the hell apple? Apparently when you have optical audio hooked up to an iMac, you can't control volume form the keyboard, and the remote becomes pretty much useless, asn the volume doesn't work on that either. Are there any hacks for this?

Gossamer · Jan 22, 2007, 11:51 PM

Yeah, I've noticed that on my computer with optical out. When I select it as the output it disables the system volume, but the in-program volumes still work. You could probably figure out a way to control the volume of each application (iTunes, VLC, etc) with the remote. I think it wants the optical out to be more of a 'line out' than a normal audio out. But under Windows I can control the optical audio through the system volume.

centerchannel68 · Jan 23, 2007, 12:36 AM

It's pretty dumb. I was reading about some guy who was using itunes to control the volume, bu tthen he went to a webpage that happened to have a midi or something and it blew out his tweeters.

****ing stupid. The buttons should work on the keyboard, and system volume should still be adjuastable.... otherwise it makes the remote fairly useless.

Gossamer · Jan 23, 2007, 04:19 PM

Originally Posted by centerchannel68

The buttons should work on the keyboard, and system volume should still be adjuastable....

That's a single issue. The buttons on the keyboard don't work because the system volume is disabled. And the only way something like you mentioned could happen is if the guy's receiver is set to a high volume (dee dee dee) and iTunes set very low. I always leave iTunes set to max volume and adjust everything else via my external speakers, whether they're attached via headphone mini-plug or optical audio. The system volume on my computer never moves, so I don't miss that function when I'm using the optical out. YMMV.

indigoimac · Jan 23, 2007, 04:25 PM

Optical disables the system sound because the data output by it is not affected by volume, it's output at a constant rate

Gossamer · Jan 23, 2007, 05:23 PM

Originally Posted by indigoimac

Optical disables the system sound because the data output by it is not affected by volume, it's output at a constant rate

But on the same computer under Windows adjusting the system volume changes it via optical out.

indigoimac · Jan 23, 2007, 05:48 PM

Originally Posted by Gossamer

But on the same computer under Windows adjusting the system volume changes it via optical out.

Well then I have no idea, I believe that optical is not supposed to have amplification behind it but rather to just be transmitting the signal, maybe the Windows driver plays w/ this somehow and OSX maintains what I always thought was the industry standard.

Eriamjh · Jan 23, 2007, 06:15 PM

Wouldn't optical out be "line level" and require and amplifer to modify?

indigoimac · Jan 23, 2007, 06:33 PM

Originally Posted by Eriamjh

Wouldn't optical out be "line level" and require and amplifier to modify?

That's the term I've been looking for, this is my understanding off it and digital coax as well, could be wrong though.

Gossamer · Jan 23, 2007, 11:30 PM

Originally Posted by Gossamer

You could probably figure out a way to control the volume of each application (iTunes, VLC, etc) with the remote. I think it wants the optical out to be more of a 'line out' than a normal audio out.

Originally Posted by Eriamjh

Wouldn't optical out be "line level" and require and amplifer to modify?

Originally Posted by indigoimac

That's the term I've been looking for, this is my understanding off it and digital coax as well, could be wrong though.

But if it was a true 'line level' then in-application volume settings shouldn't be able to change it at all, which they do.

Here's a little discussion about it.

P · Jan 24, 2007, 10:19 AM

Optical audio out - or rather SPDIF, which is what the interface is called, optical or coaxial - is somewhat more complex than you'd think. The key is the "D"-bit - digital. The idea is that the audio should stay in the original form until it gets to the amplifier, where it is decoded and amplified in one stage, with transmission to generate noise. Originally, this was intended for CD-players, where the digital audio from the CD (in PCM format) was sent to the amplifier. The audio thus sent was the original file on the CD, unmodified. For this reason, you couldn't modify the volume on the CD, only on the amplifier. If you think about how a home stereo system works, that's the standard way of working - the tape deck or the radio doesn't have a separate audio control either, it's all in the amplifier. SPDIF went on to be expanded for use with AC3 and DDS, the format used for 5.1 sound on DVDs. The same principle applies - volume control is on the amplifier.

On a computer, it gets more complex. Not all sound is in AC3 or PCM format to begin with, so the audio driver has to generate the PCM sound (to generate AC3 or DTS sound, you need a special driver or hardware live encoding on the sound board. It is called "Dolby Digital Live" and "DTS Connect", respecitively. It is a very useful, but rather unusual, feature). When generating the PCM sound, the audio driver CAN apply a volume setting. Apple doesn't - it encodes the PCM sound at some set, rather high, value.

On a Windows PC it may or may not work the same way, it depends on the driver. Most audio boards and CD/DVD-players have SPDIF passhtrough ports - if you connect this lead and set the audio driver to use SPDIF passthrough, you get the same effect when playing a CD or DVD. If you play a DVD without this lead connected (by letting the computer decode the DVD audio in software) you can usually get the same effect, by selecting SPDIF passthrough in the settings.

It becomes a little more complex when you're playing a CD - does the software DVD player read the PCM and pass it through to SPDIF? It doesn't have to, it could just as well decode it and send it to the audio driver. The audio driver will then reencode it into PCM sound for transmission - which is what it does with all other sound, obviously.

So, should the audio driver apply the volume control when encoding the PCM? It's convenient for the user to be able to control the volume like he's used to, but the downside is that the quality drops, and audio sent through SPDIF passthrough will be louder. The user will be forced to turn the amplifier volume up and down to maintain a consistent volume. Personally, I think that Apple is doing the right thing - I'd rather get maximum quality and control the audio volume with the amplifier remote. YMMV.