8 Replies Latest reply: Apr 16, 2008 4:22 AM by DaddyPaycheck
oregano Level 1 Level 1 (0 points)
Why doesn't volume control work on my MacMini?

In the Sound preferences panel, the Output Volume slider and the Mute checkbox are grayed out and can't be changed. The Apple Remote and Wireless Keyboard volume controls also don't work. The ghostly volume icon appears on screen, but with the universal "you can't do that" symbol (circle with line through it) next to the volume indicator.

I can change the volume from the slider in the menu bar, and from the slider in iTunes, or within other applications.

I'm using the mini TOSLink optical out. I'm not sure if this problem also occurs if I plug in an analog connection instead. I currently don't have any USB audio devices plugged in. I believe it has worked in the past, but can't say for sure.

The Model Identifier is Macmini2,1,
The BootRom version is MM21.009A.B00.
The System Version is Mac OS X 10.5.2 (9C7010)
The Audio (Built-in) section of System Profiler reads:
Intel High Definition Audio:

Device ID: 0x83847680
Audio ID: 8
Available Devices:
Headphone:
Connection: Combo
Speaker:
Connection: Internal
Line In:
Connection: Combo
S/P-DIF Out:
Connection: Combo
S/P-DIF In:
Connection: Combo

Message was edited by: oregano

mac mini Core 2 Duo 2.0 Ghz, 2GB Ram, Mac OS X (10.5.2), Using TOSLink audio out
  • DaddyPaycheck Level 6 Level 6 (16,035 points)
    Hi oregano-

    That is how it works. You cannot change the volume of a digital signal while it is digital-it must first be decoded back into an analog signal before volume control can be applied.

    The volume control is done via the amplifier that the digital input feeds.

    Luck-

    -DaddyPaycheck
  • oregano Level 1 Level 1 (0 points)
    Mr. Paycheck,

    Although that's what I suspected at first thought, I don't buy it. If that's the case, then why do the sliders in the menu bar and iTunes work?

    Stranger still, right now I'm listening via Airtunes to my Airport Express, and I can use the slider in iTunes, but not in the menu bar.

    I suspect that there is a means of controlling the volume digitally, perhaps by a volume parameter in the TOSLink protocol, but it seems to be implemented unevenly in the different components of software that can control volume, perhaps so they stay out of each others way. When using iTunes, I count 6 different possible ways of controlling volume within the Mac:
    --Volume Adjusment in Get Info screen for the song
    --ITunes slider
    --Menu bar slider
    --Keyboard shortcuts
    --Apple Remote
    --Default slider in control panel

    It might be that it's hard to keep these different methods from stepping on each other's toes. I wonder if this is a mini thing, or if other Macs act this way, too.

    Thanks for your reply.

    This weekend I'll wrestle an analog connection in place and see if I get my various volume controls back.
  • DaddyPaycheck Level 6 Level 6 (16,035 points)
    Hi oregano-

    When you use the sliders, you adjust the volume relative to the output within the software and prior to the digital output. The digital output volume itself is fixed.

    I am not familiar with a volume control within the TosLink or S/PDIF optical protocols-could you please provide me with a link?

    Luck-

    -DaddyPaycheck
  • Boece Level 5 Level 5 (6,245 points)
    DP,

    Could you have a look at this program from Prosoft/Joesoft and see if it adds anything to the "mix"? (Though I suspect your initial analysis is spot on.) Thanks!

    http://discussions.apple.com/message.jspa?messageID=7011801#7011801
  • DaddyPaycheck Level 6 Level 6 (16,035 points)
    Hi Boece-

    For you anything.

    That program looks pretty cool, although all of those adjustments will AKAIK be made in software prior to final output. Doing so will tax the resources of whatever system it is being run on. Some of what it does looks like it could be ear candy, however it would seem to solve the problem as posted.

    I cannot get to a Mini that is configured and set up to use optical output any time soon. Perhaps the OP would like to give it a go and report back :-)


    Later-

    -DaddyPaycheck
  • oregano Level 1 Level 1 (0 points)
    Thanks for the reply DP,

    I think you're right. The "system" sliders seem to govern what the audio hardware supports, while the iTunes sliders manipulate the bits in software. As you say, this can drive up CPU usage. I wonder if it also affects the overall quality of the output at low volumes. I was just hoping the loss of control in optical mode might be one of those little annoyances that might be "fixed" in an Apple software update, someday.

    My comment on the TOSLink protocol was rank speculation. With a bit a of Wikipediaing, I found that TOSLink audio is S/PDIF over optical, (but you knew that) and the audio protocol used is AES/EBU. The page for AES/EBU doesn't mention any volume parameters, but there is a channel status bit which yields a 24byte block that can be used in various ways. Since it's an audio spec, if controlling overall volume were one of those common uses, I'd think they'd have mentioned it. Since it has to interface with all kinds and vintages of consumer equipment, there isn't really any room for Apple to get creative here. There is a compressed and uncompressed mode for S/PDIF. Perhaps the compressed mode could allow control of overall volume?

    Poking around, a couple of other discoveries:
    --Plugging headphones into the audio out of my mini does indeed give me my mini's volume controls back, on all fronts. I like the optical though. Gives me that George Jetson techno rush.
    --The menu bar slider does not work in optical mode, as I thought it did, further weakening my argument.

    Does anyone know if the system volume can be controlled in optical mode on any Mac? Or any device for that matter?
  • oregano Level 1 Level 1 (0 points)
    Hi Boece,

    Looks like a neat program, but from the feature sheet, it doesn't seem allow volume control via apple remote. It is a nice example, however, of DPs point of the difference between manipulating bits in software vs. the audio chip.
  • DaddyPaycheck Level 6 Level 6 (16,035 points)
    Hi oregano-

    No worries. I do believe that a User should seek out as much information on their own as possible and you have done that nicely.

    As I am pondering this it does seem like TOSLink and S/PDIF are technologies that were born in other industries and used a particular way for 20 odd years and are now adapted to a similar and totally different use.

    An example, sort of, is cable TV. All of the channels pretty much come in at once and at one signal level. It is up to your TV, VCR or other device with built-in tuner to decode and control what happens to those signals.

    Thus it is the same with TOSLink. I am pretty certain that the technology was adapted by the music industry to allow as many bits and bytes as possible to flow from one device to another. It is a digital stream and as such a user, let's say a musician, would not want anything to alter that signal until it was fully transmitted in digital form from one device to another. Up until just recently the target device was usually an ADAT storage tape.

    So we are talking about taking what is and has been a transfer technology and protocol for all of these years and now using it as control circuitry.

    It ain't gonna happen. Besides, there are other protocols and technologies better suited to controlling an audio signal, and they have been around WAY longer than anything digital :-)


    I now hop off the box...

    -DaddyPaycheck