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  1. #1

    Basic digital output questions ...

    Hi all,

    while I'm an old-time Squeezebox user (Boom, Radio, Touch), I've always
    used the analog outputs of my Touch to feed into a NAD C355BEE
    amplifier and I understand that the DAC of the Touch does the
    digital/analog conversion.

    Now - due to a redesign of the living room multi media setup - the
    Touch feeds a Pioneer/Onkyo stereo receiver using digital TOSLINK.

    Now I'm wondering ... is the Touch "just" a network transport and
    receives the audio files and passes them 1:1 via digital TOSLINK to the
    receiver or is the Touch actually "doing" anything with the data? What
    about different audio formats? What is passed on 1:1, what is
    transcoded - if at all?

    Thanks in advance for any explanations. I'm also happy to get
    redirected to some older thread or explanation in some wiki or similar.

    Greetings,
    Stefan

  2. #2
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    Quote Originally Posted by sbellon View Post
    Hi all,

    while I'm an old-time Squeezebox user (Boom, Radio, Touch), I've always
    used the analog outputs of my Touch to feed into a NAD C355BEE
    amplifier and I understand that the DAC of the Touch does the
    digital/analog conversion.

    Now - due to a redesign of the living room multi media setup - the
    Touch feeds a Pioneer/Onkyo stereo receiver using digital TOSLINK.

    Now I'm wondering ... is the Touch "just" a network transport and
    receives the audio files and passes them 1:1 via digital TOSLINK to the
    receiver or is the Touch actually "doing" anything with the data? What
    about different audio formats? What is passed on 1:1, what is
    transcoded - if at all?

    Thanks in advance for any explanations. I'm also happy to get
    redirected to some older thread or explanation in some wiki or similar.

    Greetings,
    Stefan
    Correct. Now the TOUCH is simply a network transport. It delivers the digital file to the DAC. There is no digital > analog > digital conversion going on inside the TOUCH. Very few, if any, things are transcoded. The only thing I can think of that might be transcoded by the TOUCH would be any file (FLAC or ALAC or WAV) that is greater than a 24/192 file. The TOUCH can handle up to 24/96 natively.
    Home: VBA 4TB (2.5)>LMS 7.9.2>Transporter, Touch, Boom, Radio (all ethernet)
    Cottage: VBA 3TB (2.4)>LMS 7.9.1>Touch>Benchmark DAC I, Boom, Radio w/Battery (ethernet, Radio WIFI)
    Office: Win10(64)>LMS 7.9.2>Squeezelite
    The Wild (no internet): PiCorePlayer 4.0 on rPi 3B+, hifiberry Dac+Pro, 4TB USB (LMS & Squeezelite)
    Controllers: iPhone6 & iPadAir2 (iPeng), CONTROLLER, or SqueezePlay 7.8 on Win10(64) laptop
    Files: ripping: dbpa > FLAC; post-rip: mp3tag, PerfectTunes; Streaming: Spotify

  3. #3
    First of all, thanks a lot for your reply.

    Yes, that there's no D/A and A/D conversion is clear. My question is rather regarding the transcoding.

    The native capabilities of the Touch and those of the DAC obviously need not be the same. So, the Touch could play files natively the DAC cannot and/or vice versa. If Touch and DAC can handle a file, the Touch could pass on that data 1:1 via TOSLINK to the DAC. Does it do it?

    However what happens, if the DAC cannot play a certain file type the Touch can (e.g. Ogg Vorbis)? Will the Touch just stream it and the DAC plays silence?

    And vice versa, the Touch can play up to 24bit/96KHz ... what if I stream a 24bit/192KHz file to the Touch and the DAC could handle it? Will the Touch just pass it on bit-by-bit or will it refuse to play it (or transcode it to 24bit/96KHz)?

  4. #4
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    Quote Originally Posted by sbellon View Post
    First of all, thanks a lot for your reply.

    Yes, that there's no D/A and A/D conversion is clear. My question is rather regarding the transcoding.

    The native capabilities of the Touch and those of the DAC obviously need not be the same. So, the Touch could play files natively the DAC cannot and/or vice versa. If Touch and DAC can handle a file, the Touch could pass on that data 1:1 via TOSLINK to the DAC. Does it do it?

    However what happens, if the DAC cannot play a certain file type the Touch can (e.g. Ogg Vorbis)? Will the Touch just stream it and the DAC plays silence?

    And vice versa, the Touch can play up to 24bit/96KHz ... what if I stream a 24bit/192KHz file to the Touch and the DAC could handle it? Will the Touch just pass it on bit-by-bit or will it refuse to play it (or transcode it to 24bit/96KHz)?
    If the Touch can play a file and the DAC can play a file, it will be passed on 1:1 to the DAC. If the DAC can handle 24/96, I know the TOUCH won't pass on 24/192 (without the EDO applet). Thus the 24/192 file will be transcoded to 24/96 when sent to the Touch even though the DAC can handle 24/192.

    Not 100% sure about all the permutations you're asking about. But most can be tested by simply playing the file and seeing what happens. In LMS logfiles you can see info about transcoding. Forget exactly where (maybe SERVER logs or PLAYER logs).
    Home: VBA 4TB (2.5)>LMS 7.9.2>Transporter, Touch, Boom, Radio (all ethernet)
    Cottage: VBA 3TB (2.4)>LMS 7.9.1>Touch>Benchmark DAC I, Boom, Radio w/Battery (ethernet, Radio WIFI)
    Office: Win10(64)>LMS 7.9.2>Squeezelite
    The Wild (no internet): PiCorePlayer 4.0 on rPi 3B+, hifiberry Dac+Pro, 4TB USB (LMS & Squeezelite)
    Controllers: iPhone6 & iPadAir2 (iPeng), CONTROLLER, or SqueezePlay 7.8 on Win10(64) laptop
    Files: ripping: dbpa > FLAC; post-rip: mp3tag, PerfectTunes; Streaming: Spotify

  5. #5
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    Actually, the Touch will decode the file (unless it's in a format it cannot handle, then the server will and stream the (trans/de)coded file to the touch), and send uncompressed lossless PCM audio to the DAC via TOSLINK / SPDIF
    A DAC doesn't know anything about audio formats - it's digital data stream in, analog signal out

  6. #6
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    Quote Originally Posted by Roland0 View Post
    Actually, the Touch will decode the file (unless it's in a format it cannot handle, then the server will and stream the (trans/de)coded file to the touch), and send uncompressed lossless PCM audio to the DAC via TOSLINK / SPDIF
    A DAC doesn't know anything about audio formats - it's digital data stream in, analog signal out
    I *think* I agree with your statements above regarding PCM audio is what the DAC is streaming. But to be clear, do you agree that the TOUCH can't handle 24/192 (without EDO). Consequently, LMS will convert a 24/192 file to 24/96 *even though* the DAC itself could handle 24/192.
    Home: VBA 4TB (2.5)>LMS 7.9.2>Transporter, Touch, Boom, Radio (all ethernet)
    Cottage: VBA 3TB (2.4)>LMS 7.9.1>Touch>Benchmark DAC I, Boom, Radio w/Battery (ethernet, Radio WIFI)
    Office: Win10(64)>LMS 7.9.2>Squeezelite
    The Wild (no internet): PiCorePlayer 4.0 on rPi 3B+, hifiberry Dac+Pro, 4TB USB (LMS & Squeezelite)
    Controllers: iPhone6 & iPadAir2 (iPeng), CONTROLLER, or SqueezePlay 7.8 on Win10(64) laptop
    Files: ripping: dbpa > FLAC; post-rip: mp3tag, PerfectTunes; Streaming: Spotify

  7. #7
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    Quote Originally Posted by garym View Post
    But to be clear, do you agree that the TOUCH can't handle 24/192 (without EDO). Consequently, LMS will convert a 24/192 file to 24/96 *even though* the DAC itself could handle 24/192.
    Yes (EDO = Enhanced Digital Output to external DAC). Each device (e.g. Touch) announces it's capabilities (including supported sample rates etc.) to the server, if the audio sample rate isn't supported, the server will downsample.
    Example from squeezelite + USB DAC:
    Code:
    sendHELO:140 cap: Model=squeezelite,AccuratePlayPoints=1,HasDigitalOut=1,HasPolarityInversion=1,Firmware=v1.8.6-945,ModelName=SqueezeLite,MaxSampleRate=48000,alc,wma,wmap,wmal,aac,ogg,flc,aif,pcm,mp3,loc

  8. #8
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    Quote Originally Posted by Roland0 View Post
    Yes (EDO = Enhanced Digital Output to external DAC). Each device (e.g. Touch) announces it's capabilities (including supported sample rates etc.) to the server, if the audio sample rate isn't supported, the server will downsample.
    Example from squeezelite + USB DAC:
    Code:
    sendHELO:140 cap: Model=squeezelite,AccuratePlayPoints=1,HasDigitalOut=1,HasPolarityInversion=1,Firmware=v1.8.6-945,ModelName=SqueezeLite,MaxSampleRate=48000,alc,wma,wmap,wmal,aac,ogg,flc,aif,pcm,mp3,loc
    Thanks!
    Home: VBA 4TB (2.5)>LMS 7.9.2>Transporter, Touch, Boom, Radio (all ethernet)
    Cottage: VBA 3TB (2.4)>LMS 7.9.1>Touch>Benchmark DAC I, Boom, Radio w/Battery (ethernet, Radio WIFI)
    Office: Win10(64)>LMS 7.9.2>Squeezelite
    The Wild (no internet): PiCorePlayer 4.0 on rPi 3B+, hifiberry Dac+Pro, 4TB USB (LMS & Squeezelite)
    Controllers: iPhone6 & iPadAir2 (iPeng), CONTROLLER, or SqueezePlay 7.8 on Win10(64) laptop
    Files: ripping: dbpa > FLAC; post-rip: mp3tag, PerfectTunes; Streaming: Spotify

  9. #9
    Ok, thanks for the clarification. Does that mean that over TOSLINK only PCM is specified? When I said DAC ... I have a stereo receiver that claims to be able to handle various formats and sample rates, etc. but from your understanding, this only applies to native playback or maybe network playback, but digital optical in via TOSLINK is always PCM?

  10. #10
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    Quote Originally Posted by sbellon View Post
    Ok, thanks for the clarification. Does that mean that over TOSLINK only PCM is specified?
    Yes (details)

    When I said DAC ... I have a stereo receiver that claims to be able to handle various formats and sample rates, etc. but from your understanding, this only applies to native playback or maybe network playback, but digital optical in via TOSLINK is always PCM?
    Sure, multi-functional devices may have components which will transform <something> to PCM. However, SPDIF is just for transporting PCM, so the device can only process this bitstream (e.g. up / downsample)
    Sample rate is a property of the PCM stream (the data rate), so this has to be supported by the data link layer (which is part of SPDIF)

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