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2004-07-21, 16:58
> -----Original Message-----
> From: discuss-bounces (AT) lists (DOT) slimdevices.com
> [mailto:discuss-bounces (AT) lists (DOT) slimdevices.com] On Behalf Of Sean Adams
> Sent: 21 July 2004 23:52
> To: Slim Devices Discussion
> Subject: [slim] How does lossless work?
>
>
> On Jul 21, 2004, at 2:43 PM, Jacob Potter wrote:
>
> > On Wed, 21 Jul 2004 13:50:46 -0700, kdf
> <slim-mail (AT) deane-freeman (DOT) com>
> > wrote:
> >> internal to the squeezebox, the data is either MP3 or PCM
> depending
> >> on the data that was sent from the server. There is hardware to
> >> handle both.
> >
> > Specifically, the data from SlimServer to the Squeezebox
> can be either
> > MP3, or PCM at any of 11/22/32/44.1/48 KHz, 8/16/24/32-bit, mono or
> > stereo, big or little endian. Any conversions for the DAC or S/PDIF
> > are done in the Squeezebox itself.
> >
>
> Close - actually mp3 is supported with 20 bits of resolution
> and at all sample rates (32, 44.1, 48) and all mp3 bit rates
> (32..320Kbps). Most s/pdif receivers will only look at 16 of
> those 20 bits. However, 20 bits d/a is always used in
> Squeezebox's DAC. Incidentally this might for some be a
> reason to favor Squeezebox's internal DAC over a particular
> s/pdif DAC.
>
> PCM (whether FLAC, WAV, AIFF) is currently supported just for
> CD data rates, ie 44.1KHz, 16 bits per sample. However, this
> is only because we haven't had much interest in other
> formats. The hardware is capable of PCM at arbitrary sample
> rates up to 48KHz, and 20 bits per sample, but we haven't
> added support for that yet due to having higher priorities
> for software. Additional bits (for 20 bits output) ** are
> used ** for 16-bit audio when the volume control is below max
> level (to increase s/n ratio).

Interesting stuff.

Is there any change of getting hold of a circuit diagram of the squeezebox
as I'm interested in experimenting with some mods (primarily analogue output
stage) ?

R.

seanadams
2004-07-21, 17:26
> Interesting stuff.
>
> Is there any change of getting hold of a circuit diagram of the
> squeezebox
> as I'm interested in experimenting with some mods (primarily analogue
> output
> stage) ?
>

Sure, here it is. Please also get the mas35x9 data sheet from micronas.
This is mostly the same as their reference schematic but you should
study the data sheet to see the capabilities of the chip. Also see
mas35x9.pm in our source code to see what features we're using. There
are quite a few features we don't use that might be of interest, for
example mixing another analog source in with the audio via the
geekport. One fun project might be an FM tuner controlled by i2c that
uses this mechanism.

If you want to connect a different DAC you can do so using the SOC,
SOI, and SOD pins. Note that two of these pins are easily accessible at
the 74HC125. The other pin unfortunately is not brought out but if you
are extremely agile with a soldering iron, it is quite possible to
solder directly onto the chip.

Legal C.M.A: this does not imply any license to implement this design
for any purpose. Just sharing it so you can hack on it.