lossless recording with audio line in hacked as SPDIF

[maxime.levesque]

 I have a high qualidy audio interface with SPDIF
output (optical and coaxial). This interface has high
quality preamps and ADC (analog to digital converter).

 I had chosen to get an iRiver H340 for it's optical
line in, but I'm reluctant since the H models are
discontinued (in north america at least).

 I was wondering if it would be feasable that
rockbox interpret an SPDIF stream coming in from it's ADC
(audio line in) and save it as WAV.

   ---SP/DIF-Coaxial---> auidio-line-in ---> ADC--->

 I imagine this could be done with a custom codec
that would do nothing, but perhaps a simple
conversion of incoming stream of PCM values.

 such a codec could enable all rockbox ports to
use the audio line in as an SPDIF in.

 Is this possible ? I'm no expert of the SPDIF
protocol, so perhaps it's just not possible,
but it would be a killer feature for recording
with high quality analog and ADC gear.

  If it's at all possible, I could offer some help,
 I'm a programmer and have dealt with codecs
 before (VoIP codecs).

  Thanks

   Max

[Febs]

The H340 does not have an optical input.  Only the H1XX series has the optical in.

[pabouk]

I had chosen to get an iRiver H340 for it's optical
line in...

As Febs wrote the iriver H100 series are the only portable players supported by Rockbox which have S/PDIF.

I was wondering if it would be feasable that
rockbox interpret an SPDIF stream coming in from it's ADC
(audio line in) and save it as WAV.

Unfortunately it is not possible on most of the players. Because S/PDIF transfers 64 bits per one stereo sample and it uses a modulation with up to 2 transitions per bit.  (see AES/EBU)

So for example 44.1 kHz sampled data (for example from an audio CD) would produce:
44100 * 64 * 2 = 5644800 possible transitions per second. It means that the ADC must run at least at approximately 5.65 MHz sampling rate! I am almost sure that none of the portable players on the market has such a ADC and even if you find such a player it is impossible to process the data at such speed in real time by the poor CPUs used in the players.

[maxime.levesque]

   Aahh it worked so well in theory !  

 Except for the small piece of theory that says the
sampling rate of the ADC and CPU throughput is insufficient !

 I was ready to get myself a H340, but then
started shopping online, and found it nowhere
in North America (I'm in Canada).
 And from looking at the mystic river forum,
it looks like the product is defunct, and
iRiver is not interrested in producing players
loaded with features. But the H340 specs
have made me want an SPDIF line in (and out) !
The problem is, no one wants to make them
(not even iRiver anymore).

  Besides from the practical problem of just finding an
H340 for sale, I figure it will be a PITA, if I ever need
to use the warranty (if I need to import it).
Then there's the US version that is watered down
(from what the folks say at mystic reiver).
Also, whatever unit I manage to get will have sat
on a shelf for a few years, apparently not good for the
battery....

 So I had my mind set on an iAudio x5, and started
dreaming of a way to get an SPDIF line in by hacking
a line in codec... Well it was a wet dream....

  Thanks anyways for the info !

 Whatever unit I eventually get,
 I will definitely try  Rockbox !

    Max

[AlexP]

Again, the H300 series DOES NOT have optical in or out.  Only the H100 series has that.

[mborus]

Again, the H300 series DOES NOT have optical in or out.  Only the H100 series has that.

As far as I understood it maxime.levesque wanted to connect a coax digital signal to the analog line in and have rockbox sample and interpret the signal this way.

This is not likely to happen and I don't understand myself why he doesn't buy a used H140 or H120 instead - as this portable doesn't need hacking to record WAVs of the digital optical input. H120s are really easy to get, you just have to watch ebay for a few weeks and one will come up. There's one selling at EUR 200 / Buy now on ebay Germany at the moment.

[AlexP]

OK, I understood it as the H300 making him want an spdif, but him not getting it for other reasons, and then wanting to get an x5 to connect a coax digital signal to the analog line in and have rockbox sample and interpret.

Either way, you are right - if you want a spdif input try and get a H1x0.