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  1. #1
    Mark Bennett
    Guest

    Squeezebox/External DAC - technical issues

    Tonight we tried again to connect the Squeezebox up to an
    external DAC with a high end sound system behind it.

    In this post I'm going to focus on the ongoing technical
    issues. I want to make these completely separate from any
    subjective discussion about audio quality, otherwise it
    will become unproductive. I'll discuss audio quality in a
    separate post (see "Squeezebox/External DAC - audio quality"
    thread).

    At the end of the session we really have three technical
    problems which would prevent/hinder the use of this
    combination of equipment.

    First of all, let me add some context. The only DAC we
    have access to is a high-end DAC. The sort of high end where
    the designers don't trust complex digital circuits....
    The PLL for this DAC is a completely discrete design. It has
    a very slow acquisition time, and extremely high stability.
    Along with this comes an extreme intolerance for absolute
    frequency error. The DAC does work perfectly well with a CD
    transport (AudioLab CDM8000 MK2 - 44.1KHz) and a DAB tuner
    (48KHz I think).

    So on to the issues:

    1) We just could not get the DAC to lock onto the output
    of the squeezebox. Admittedly we only tried Flac and Ogg,
    with client side decoding. In hindsight we should also
    have tried WAV direct from the server, but I didn't think
    this would be different. (It might not be.)

    However this doesn't look like a hardware problem. When
    playing high bit-rate MP3's (lame encoded, 320kb/s) the
    digital output locked quickly and reliably.

    To me this sounds that the digital output frequency is
    probably still not quite right for uncompressed audio
    streams.

    2) When the Squeezebox is actually stopped there is no signal
    output on the digital out. This means that the PLL loses
    lock and we lost the first few seconds of music when
    initially playing music from stop while the PLL locked.

    By contrast the Audiolab CD transport output a silence code
    all the time it was turned on, whether it was in stop or
    pause. (We didn't think to try pause on the SB - should
    have done in hindsight.)

    This issue should affect anyone using an external DAC, is
    anyone else seeing this?

    3) The digital output also seemed to stop when skipping forward
    or backward to next/previous tracks. This showed by the DAC
    briefly flashing that it had lost input signal during the
    transition.

    Fortunately since the frequency didn't have time to drift
    we didn't lose any music, so this is an annoyance rather than
    a real problem (especially compared to 1) & 2).

    Again the CD transport's behaviour was immaculate. Again, this
    should probably affect most DAC's unless this one has an
    untypically quick loss of input detector. Is anyone else
    seeing this?

  2. #2
    Stuart Hickinbottom
    Guest

    Squeezebox/External DAC - technical issues

    Thanks for the evaulation, very interesting. I'd be interested in your
    opinion update when you have heard FLACs though it.

    I have my SB connected optically to an external DAC (actually within a
    not-very-new Technics digital integrated amplifier).

    I can play FLACs through this arrangement - the DAC locks on successfully
    at 44.1KHz.

    When my SB is paused or stopped I get no digital output and the DAC loses
    lock. This DAC seems to lock on very quickly, however, so I don't seem to
    lose anything when I restart playing.

    I also get it losing sync juring next/prev track, and also periodically
    (but not continually) when fastforwarding/reversing though a track.

    I don't have it losing sync between tracks when playing normally from one
    track to the next.

    It would be quite nice for me too if it played silence when there was no
    real signal to send as my DAC has some kind of an internal relay that I
    can hear clicking on and off when it's gaining and losing sync. Apart from
    that, though, I think it's working well for me under normal playing
    conditions.

    Stuart

    On Wed, 17 Mar 2004 22:45:51 +0000, Mark Bennett <mark (AT) markandliz (DOT) co.uk>
    wrote:

    >
    > Tonight we tried again to connect the Squeezebox up to an
    > external DAC with a high end sound system behind it.
    >
    > In this post I'm going to focus on the ongoing technical
    > issues. I want to make these completely separate from any
    > subjective discussion about audio quality, otherwise it
    > will become unproductive. I'll discuss audio quality in a
    > separate post (see "Squeezebox/External DAC - audio quality"
    > thread).
    >
    > At the end of the session we really have three technical
    > problems which would prevent/hinder the use of this
    > combination of equipment.
    >
    > First of all, let me add some context. The only DAC we
    > have access to is a high-end DAC. The sort of high end where
    > the designers don't trust complex digital circuits....
    > The PLL for this DAC is a completely discrete design. It has
    > a very slow acquisition time, and extremely high stability.
    > Along with this comes an extreme intolerance for absolute
    > frequency error. The DAC does work perfectly well with a CD
    > transport (AudioLab CDM8000 MK2 - 44.1KHz) and a DAB tuner
    > (48KHz I think).
    >
    > So on to the issues:
    >
    > 1) We just could not get the DAC to lock onto the output
    > of the squeezebox. Admittedly we only tried Flac and Ogg,
    > with client side decoding. In hindsight we should also
    > have tried WAV direct from the server, but I didn't think
    > this would be different. (It might not be.)
    >
    > However this doesn't look like a hardware problem. When
    > playing high bit-rate MP3's (lame encoded, 320kb/s) the
    > digital output locked quickly and reliably.
    >
    > To me this sounds that the digital output frequency is
    > probably still not quite right for uncompressed audio
    > streams. 2) When the Squeezebox is actually stopped there is no signal
    > output on the digital out. This means that the PLL loses
    > lock and we lost the first few seconds of music when
    > initially playing music from stop while the PLL locked.
    >
    > By contrast the Audiolab CD transport output a silence code
    > all the time it was turned on, whether it was in stop or
    > pause. (We didn't think to try pause on the SB - should
    > have done in hindsight.)
    >
    > This issue should affect anyone using an external DAC, is
    > anyone else seeing this?
    >
    > 3) The digital output also seemed to stop when skipping forward
    > or backward to next/previous tracks. This showed by the DAC
    > briefly flashing that it had lost input signal during the
    > transition.
    >
    > Fortunately since the frequency didn't have time to drift
    > we didn't lose any music, so this is an annoyance rather than
    > a real problem (especially compared to 1) & 2).
    >
    > Again the CD transport's behaviour was immaculate. Again, this
    > should probably affect most DAC's unless this one has an
    > untypically quick loss of input detector. Is anyone else
    > seeing this?
    >
    >
    >
    >
    >

  3. #3
    Gadfly, Former Founder Slim Devices dean's Avatar
    Join Date
    Apr 2005
    Location
    San Francisco, CA
    Posts
    4,427

    Squeezebox/External DAC - technical issues

    The lack of active S/PDIF at the beginnings and endings of tracks (and
    while fast forwarding) is known and will be addressed soon. Thanks for
    your patience...

    -dean

    On Mar 17, 2004, at 4:36 PM, Stuart Hickinbottom wrote:

    > Thanks for the evaulation, very interesting. I'd be interested in your
    > opinion update when you have heard FLACs though it.
    >
    > I have my SB connected optically to an external DAC (actually within a
    > not-very-new Technics digital integrated amplifier).
    >
    > I can play FLACs through this arrangement - the DAC locks on
    > successfully at 44.1KHz.
    >
    > When my SB is paused or stopped I get no digital output and the DAC
    > loses lock. This DAC seems to lock on very quickly, however, so I
    > don't seem to lose anything when I restart playing.
    >
    > I also get it losing sync juring next/prev track, and also
    > periodically (but not continually) when fastforwarding/reversing
    > though a track.
    >
    > I don't have it losing sync between tracks when playing normally from
    > one track to the next.
    >
    > It would be quite nice for me too if it played silence when there was
    > no real signal to send as my DAC has some kind of an internal relay
    > that I can hear clicking on and off when it's gaining and losing sync.
    > Apart from that, though, I think it's working well for me under normal
    > playing conditions.
    >
    > Stuart
    >
    > On Wed, 17 Mar 2004 22:45:51 +0000, Mark Bennett
    > <mark (AT) markandliz (DOT) co.uk> wrote:
    >
    >>
    >> Tonight we tried again to connect the Squeezebox up to an
    >> external DAC with a high end sound system behind it.
    >>
    >> In this post I'm going to focus on the ongoing technical
    >> issues. I want to make these completely separate from any
    >> subjective discussion about audio quality, otherwise it
    >> will become unproductive. I'll discuss audio quality in a
    >> separate post (see "Squeezebox/External DAC - audio quality"
    >> thread).
    >>
    >> At the end of the session we really have three technical
    >> problems which would prevent/hinder the use of this
    >> combination of equipment.
    >>
    >> First of all, let me add some context. The only DAC we
    >> have access to is a high-end DAC. The sort of high end where
    >> the designers don't trust complex digital circuits....
    >> The PLL for this DAC is a completely discrete design. It has
    >> a very slow acquisition time, and extremely high stability.
    >> Along with this comes an extreme intolerance for absolute
    >> frequency error. The DAC does work perfectly well with a CD
    >> transport (AudioLab CDM8000 MK2 - 44.1KHz) and a DAB tuner
    >> (48KHz I think).
    >>
    >> So on to the issues:
    >>
    >> 1) We just could not get the DAC to lock onto the output
    >> of the squeezebox. Admittedly we only tried Flac and Ogg,
    >> with client side decoding. In hindsight we should also
    >> have tried WAV direct from the server, but I didn't think
    >> this would be different. (It might not be.)
    >>
    >> However this doesn't look like a hardware problem. When
    >> playing high bit-rate MP3's (lame encoded, 320kb/s) the
    >> digital output locked quickly and reliably.
    >>
    >> To me this sounds that the digital output frequency is
    >> probably still not quite right for uncompressed audio
    >> streams. 2) When the Squeezebox is actually stopped there is no
    >> signal
    >> output on the digital out. This means that the PLL loses
    >> lock and we lost the first few seconds of music when
    >> initially playing music from stop while the PLL locked.
    >>
    >> By contrast the Audiolab CD transport output a silence code
    >> all the time it was turned on, whether it was in stop or
    >> pause. (We didn't think to try pause on the SB - should
    >> have done in hindsight.)
    >>
    >> This issue should affect anyone using an external DAC, is
    >> anyone else seeing this?
    >>
    >> 3) The digital output also seemed to stop when skipping forward
    >> or backward to next/previous tracks. This showed by the DAC
    >> briefly flashing that it had lost input signal during the
    >> transition.
    >>
    >> Fortunately since the frequency didn't have time to drift
    >> we didn't lose any music, so this is an annoyance rather than
    >> a real problem (especially compared to 1) & 2).
    >>
    >> Again the CD transport's behaviour was immaculate. Again, this
    >> should probably affect most DAC's unless this one has an
    >> untypically quick loss of input detector. Is anyone else
    >> seeing this?
    >>
    >>
    >>
    >>
    >>

  4. #4
    Pat Farrell
    Guest

    Squeezebox/External DAC - technical issues

    At 05:45 PM 3/17/2004, Mark Bennett wrote:
    >Tonight we tried again to connect the Squeezebox up to an
    >external DAC with a high end sound system behind it.
    >1) We just could not get the DAC to lock onto the output
    > of the squeezebox. Admittedly we only tried Flac and Ogg,
    > with client side decoding.


    What cabling did you use? toslink? SPDIF?
    All my music is FLAC, works mostly great.

    >When the Squeezebox is actually stopped there is no signal
    > output on the digital out. This means that the PLL loses...
    > This issue should affect anyone using an external DAC, is
    > anyone else seeing this?


    Not on my setup, Benchmark DAC-1


    > should probably affect most DAC's unless this one has an
    > untypically quick loss of input detector. Is anyone else
    > seeing this?


    I found the coax SPdif connection to be flakey. But there were threads
    on it being fixed in a near future release so I have not been
    scientific about it.

    I just use the TOSlink optical connection.
    I get occasional dropouts, but in general the sound quality
    is wonderful, and the dropouts are not frequent enough to drive me nuts,
    altho they are noticable and I'm tempted to hold my breath until
    the new firmware /server ware fixes it.

    I would not be happy with the coax SPdif, but Toslink is at least OK.

    Pat

  5. #5
    Mark Bennett
    Guest

    Squeezebox/External DAC - technical issues

    So, apart from the FLAC experience, it sounds like you're
    seeing the same problems as us. I should have mentioned that
    we also do not see any problems when transitioning from
    the end of one track to the start of another.

    I suspect that the FLAC locking is due to very fussy DAC, so
    I expect that it will work for most people. We're trying to
    find the specs for the DAC, but it is now obsolete, and
    my friend isn't sure where it's instruction manual is...

    Stuart Hickinbottom wrote:
    > Thanks for the evaulation, very interesting. I'd be interested in your
    > opinion update when you have heard FLACs though it.
    >
    > I have my SB connected optically to an external DAC (actually within a
    > not-very-new Technics digital integrated amplifier).
    >
    > I can play FLACs through this arrangement - the DAC locks on
    > successfully at 44.1KHz.
    >
    > When my SB is paused or stopped I get no digital output and the DAC
    > loses lock. This DAC seems to lock on very quickly, however, so I don't
    > seem to lose anything when I restart playing.
    >
    > I also get it losing sync juring next/prev track, and also periodically
    > (but not continually) when fastforwarding/reversing though a track.
    >
    > I don't have it losing sync between tracks when playing normally from
    > one track to the next.
    >
    > It would be quite nice for me too if it played silence when there was
    > no real signal to send as my DAC has some kind of an internal relay
    > that I can hear clicking on and off when it's gaining and losing sync.
    > Apart from that, though, I think it's working well for me under normal
    > playing conditions.
    >
    > Stuart
    >

  6. #6
    Mark Bennett
    Guest

    Squeezebox/External DAC - technical issues

    Thanks for the info on this. It's good to know these are recognised
    problems that are being worked on. I can afford to be patient if I
    know something will happen - I don't think the CFO (wife) will
    sanction the expense on an external DAC for a few months!

    My friend will hold off purchasing SB until the issues are resolved.

    dean blackketter wrote:

    > The lack of active S/PDIF at the beginnings and endings of tracks (and
    > while fast forwarding) is known and will be addressed soon. Thanks for
    > your patience...
    >
    > -dean

  7. #7
    Mark Bennett
    Guest

    Squeezebox/External DAC - technical issues

    Pat Farrell wrote:

    > At 05:45 PM 3/17/2004, Mark Bennett wrote:
    >
    >> Tonight we tried again to connect the Squeezebox up to an
    >> external DAC with a high end sound system behind it.
    >> 1) We just could not get the DAC to lock onto the output
    >> of the squeezebox. Admittedly we only tried Flac and Ogg,
    >> with client side decoding.

    >
    >
    > What cabling did you use? toslink? SPDIF?
    > All my music is FLAC, works mostly great.


    We only tried the Toslink. I guess we should have tried the
    S/PDIF, but only had limited time to get things sorted. Since
    MP3 was working it seemed pretty unlikely that the Flac/toslink
    combo was a problem.

    >> When the Squeezebox is actually stopped there is no signal
    >> output on the digital out. This means that the PLL loses...
    >> This issue should affect anyone using an external DAC, is
    >> anyone else seeing this?

    >
    >
    > Not on my setup, Benchmark DAC-1


    This is interesting, especially since I have my eye on the
    same DAC at ome point in the future:-)

  8. #8
    Mark Bennett
    Guest

    Squeezebox/External DAC - technical issues

    One extra piece of information on this. I found out today that
    this DAC only has an input frequency error tolerance of 100ppm.
    For a normal 44.1kHz signal this basically means 4Hz out in
    either direction.

    Obviously this is very tight, so the clock setting in the chip
    might only need to be one count away from ideal to upset this
    DAC. Unfortunately I don't think we have any lab equipment at
    work which would allow me to measure to this degree of
    accuracy, so I don't know how I can help further.

    I guess the answer is to get access to a less fussy DAC, but
    this isn't going to happen for months, so this would be the
    end of the route as regards further testing.....

    Mark Bennett wrote:
    > So, apart from the FLAC experience, it sounds like you're
    > seeing the same problems as us. I should have mentioned that
    > we also do not see any problems when transitioning from
    > the end of one track to the start of another.
    >
    > I suspect that the FLAC locking is due to very fussy DAC, so
    > I expect that it will work for most people. We're trying to
    > find the specs for the DAC, but it is now obsolete, and
    > my friend isn't sure where it's instruction manual is...
    >
    > Stuart Hickinbottom wrote:
    >
    >> Thanks for the evaulation, very interesting. I'd be interested in
    >> your opinion update when you have heard FLACs though it.
    >>
    >> I have my SB connected optically to an external DAC (actually within
    >> a not-very-new Technics digital integrated amplifier).
    >>
    >> I can play FLACs through this arrangement - the DAC locks on
    >> successfully at 44.1KHz.
    >>
    >> When my SB is paused or stopped I get no digital output and the DAC
    >> loses lock. This DAC seems to lock on very quickly, however, so I
    >> don't seem to lose anything when I restart playing.
    >>
    >> I also get it losing sync juring next/prev track, and also
    >> periodically (but not continually) when fastforwarding/reversing
    >> though a track.
    >>
    >> I don't have it losing sync between tracks when playing normally from
    >> one track to the next.
    >>
    >> It would be quite nice for me too if it played silence when there was
    >> no real signal to send as my DAC has some kind of an internal relay
    >> that I can hear clicking on and off when it's gaining and losing
    >> sync. Apart from that, though, I think it's working well for me under
    >> normal playing conditions.
    >>
    >> Stuart
    >>

    >
    >
    >

  9. #9
    T
    Guest

    Squeezebox/External DAC - technical issues

    > One extra piece of information on this. I found out today that
    > this DAC only has an input frequency error tolerance of 100ppm.
    > For a normal 44.1kHz signal this basically means 4Hz out in
    > either direction.
    >
    > Obviously this is very tight,


    Actually, thats very loose. Too loose for professional use, anyway.

    Tom

  10. #10
    Mark Bennett
    Guest

    Squeezebox/External DAC - technical issues

    Tom,

    I think you might have mis-understood me. I'm not talking about
    jitter here, I'm talking about absolute frequency error. You can
    have 0ppm jitter (theoretically) and still have 100pm (or more)
    absolute frequency error.

    Having a tolerance of just +/-4Hz on whether the DAC will see the
    input signal or not is tiny. I bet that most professional DAC's
    are much more tolerant that this. One well respected professional
    DAC - the Benchmark DAC1 (keeps cropping up doesn't it?) seems
    to be able to lock to *any* sample rate between 28KHz and 198KHz.
    This is a massive tolerance to frequency error in terms of
    ability to lock.

    Of course, 100ppm of jitter would not be acceptable to professional
    users, nor most audiophile domestic users, but this isn't what
    I'm talking about.

    100ppm of frequency error is equivalent to a 5 minute track being,
    at most 30ms longer (or shorter) than it should be. I would be
    staggered if anyone really through they could hear this make an
    audible difference to played music.

    Of course, 100ppm of jitter would not be acceptable to professional
    users, nor most audiophile domestic users, but this isn't what
    I'm talking about.

    Cheers,
    Mark.

    T wrote:
    >>One extra piece of information on this. I found out today that
    >>this DAC only has an input frequency error tolerance of 100ppm.
    >>For a normal 44.1kHz signal this basically means 4Hz out in
    >>either direction.
    >>
    >>Obviously this is very tight,

    >
    >
    > Actually, thats very loose. Too loose for professional use, anyway.
    >
    > Tom
    >
    >

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