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  1. #1
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    LMS Volume control

    Hi there

    I've purchased a RaspberryPi with the 7 inch Touch Display and am planning to install a DAC board, etc. to end up with a Squeezebox Touch replacement.

    When I installed piCorePlayer on the RPi I was asked about output and I could see that ALSA defaults to + 3-4 dB (or something like that) and that I'd have to choose 96% to get 0 dB out, which I did.

    Suddenly I realize there's at least 4 different ways to control the volume, and I'm wondering - in which way does the LMS control it? Is it a "bit-perfect" reduction, or is it scaling in percent (not digital-friendly) ... and is dithering used, or not? Does LMS also "boost" output 3-4 dB at 100% ??

    Thanks for any response that can make me a bit wiser as to what's going on. Pointers to previous discussions is definitely OK (I did a search both here and with Google, without finding answers).

    P.S. I purchased the ApplePi DAC + Volume-Clocker, and the volume part controls the volume in a "bit-perfect" way, which presumably means it of course reduces output bits when you turn down the volume, but there's no quantization noise, etc. I find that I can control volume in LMS, as well as in piCorePlayer with the ALSA mixer, and now with the digital Volume-Clocker + finally I can also use the (analog) volume control on my integrated amplifier.

    Best regards,
    Claus

  2. #2
    Senior Member Greg Erskine's Avatar
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    hi cfuttrup,

    My advise is not the think about volume control to much... it hurts.

    Quote Originally Posted by cfuttrup View Post
    Hi there

    I've purchased a RaspberryPi with the 7 inch Touch Display and am planning to install a DAC board, etc. to end up with a Squeezebox Touch replacement.
    Welcome to the club.

    When I installed piCorePlayer on the RPi I was asked about output and I could see that ALSA defaults to + 3-4 dB (or something like that) and that I'd have to choose 96% to get 0 dB out, which I did.
    This is only concerning the built-in audio. The RPi built-in audio card is called "ALSA". I think they did this to confuse people. By default there is a 4dB gain. We have been recently playing with the "card controls" to allow this to be set to exactly 0dB rather than 96% which I think is 0.25dB.

    Suddenly I realize there's at least 4 different ways to control the volume, and I'm wondering - in which way does the LMS control it? Is it a "bit-perfect" reduction, or is it scaling in percent (not digital-friendly) ... and is dithering used, or not? Does LMS also "boost" output 3-4 dB at 100% ??
    Scary when you start thinking about this! You can set LMS to output 100% and use your analogue volume control, this is what I used to do. In the end I found, convenience won out and I use LMS volume control even though it is probably not bit perfect. I don't think LMS boosts output.

    P.S. I purchased the ApplePi DAC + Volume-Clocker, and the volume part controls the volume in a "bit-perfect" way, which presumably means it of course reduces output bits when you turn down the volume, but there's no quantization noise, etc. I find that I can control volume in LMS, as well as in piCorePlayer with the ALSA mixer, and now with the digital Volume-Clocker + finally I can also use the (analog) volume control on my integrated amplifier.
    Have you got your ApplePi DAC working? AFAIK we haven't got ApplePi DAC on the drop-down yet.

    regards
    Greg

  3. #3
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    Hi Claus,

    questions with bit-perfect belongs to the audiophile part of the Forum.

    A RPI is never bitperfect.

    cause there is no thing like bitperfect thats a audiophoolish nonsense made from people who have no clue about how a Computer works or they know it but the word bitperfect helps them to get their snakeoil sold..

  4. #4
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    Hi Greg - The ApplePi is currently sitting in customs (6 days now). Will let you know how it goes. I am also heading in the direction convenience with software volume control, but there's no need for multiple controls to each contribute with signal errors, so I guess I'll think a bit harder ... :-)

    Hi DJanGo - I don't try to misunderstand the terms, and don't mean to be talking audiophoolishly, but my sense is that the digital signal is treated as such (in digital bits and bytes). There is a major difference between this, and then running some floating point calculations (with rounding errors).

    Best regards,
    Claus

  5. #5
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    Is there anyone who knows the details about how the LMS volume control works?
    In particular if there's larger than zero dB gain in it?

  6. #6
    Senior Member pippin's Avatar
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    No, replay gain is always negative in a Squeezebox system (smaller than one as a factor, negative dB)
    ---
    learn more about iPeng, the iPhone and iPad remote for the Squeezebox and
    Logitech UE Smart Radio as well as iPeng Party, the free Party-App,
    at penguinlovesmusic.com
    New: iPeng 9, the Universal App for iPhone, iPad and Apple Watch

  7. #7
    Senior Member pippin's Avatar
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    And regarding your other questions: I believe there are ways to make either the server (Daphile) or the player (SqueezeLite settings) either but I’m not sure.
    Per default, a Squeezebox will multiply the signal value with the volume and als in addition to that with replay gain values (if enabled) on a 24 Bit value range (Independent of the Input value range).
    Other players can work differently, though. iPeng, for example, doesn’t modify the output but multiplies replay gain with the volume level and hands this to the iOS audio handling, what it does with this is hardware-dependent. I believe the AirPlay bridge, for example, works in a similar way.

    SqueezeLite has all kind of options for this. Per default I believe it multiplies eighths replay gain values (not sure if on a 24 or 32 bit scale) but uses ALSA volume for volume control, but I can remember that wrongly. I’d recommend to read the SqueezeLite documentation on this, it really has a ton of options.
    ---
    learn more about iPeng, the iPhone and iPad remote for the Squeezebox and
    Logitech UE Smart Radio as well as iPeng Party, the free Party-App,
    at penguinlovesmusic.com
    New: iPeng 9, the Universal App for iPhone, iPad and Apple Watch

  8. #8
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    Hi pippin

    Many thanks for this info, and the tip to read up about Squeezelite. Is this documentation in the wiki: http://wiki.slimdevices.com/index.php/Squeezelite ?? ... or did you mean to look elsewhere?

    Meanwhile, I found that bit-perfect volume control requires that you add some bits ... so that if f.eks. Squeezelite uses 32 bit representation, it should be able to do bit-perfect volume control, as explained here: http://www.esstech.com/files/3014/40...me-control.pdf

    Cheers,
    Claus

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