Hello,
I begin by explaining my use of the pi. I want to make it a sound server with remote control (android app) and use it’s i2s outpout, because this infercace is an emergent hifi standart, since psaudio propose an open inferface with an hdmi cable for i2s :
diyaudio.com/forums/digital- … audio.html
Moved from RaspyFi’s forum, since that’s pretty interesting.
Author: GhostMM666
Link: http://www.raspyfi.com/forum/everything-else/i2s-over-hdmi-ps-audio-and-resampling-with-sox/
Some manufacturer propose compatible board for this :
http://www.fidelix.jp/technology/I2S.html
http://www.audiophonics.fr/aune-kit-module-dentree-hdmi-vers-i2s-p-8404.html
If i understand it right we just have to connect the P5 headers of our pi to this, to obtain a good i2s outpout for hifi purpose, compatible with a growing number of equipement (for now, one of the only music server compatible is the sonore rendu : http://www.sonore.us/index7.htmland it cost nerly 1600€ with this i2s hdmi option, and also a growing list of dac)
I know that an alsa driver for i2s has been written, but i don’t know if it’s work with this?
Another question, at diyaudio they are making a dac constituate of some separate (different projects…) boards. An I2S Fifo kit, constituate of the fifo board, a clock and an isolator :
http://www.diyaudio.com/forums/digital-line-level/192465-asynchronous-i2s-fifo-project-ultimate-weapon-fight-jitter.html
They also have made a board which is an I2S to PCM converter :
http://www.diyaudio.com/forums/digital-line-level/220407-drive-nos-ad1865-62-pcm1704-02-63-tda1541-fifo-universal-i2s-pcm-driver-board.html
As they speak better than me (extract from the datashit of the board) :
« Many people still like the sound of traditional MULTIBIT audio DACs, such as AD1865/62, PCM1704/02, PCM63, TDA1541/A, and many others, because they convert digital music into analog in a different way than popular DELTA-SIGMA DACs.
However, most of those MULTIBIT DACs were designed having to work with digital filter chip through an interface we called “PCM”, which transmits left and right data simultaneously. In this case, the problem would be that the sound quality and the maximum Fs of MULTIBIT DACs can be limited by the performance of the hardware based over sampling digital filter chip due to the low internal calculating accuracy, the resource saving interpolating algorithm, and the old higher jitter hardware technology.
In order to boost the sound quality by introducing low jitter technology and to play higher Fs music, we need to get rid of the limitation of that digital filter chip by driving the MULTIBIT DAC from higher performance software base real-time up-sampling filter or high Fs music stream directly. So, we need a jitter optimized device to run MULTIBIT DAC at NOS mode from an I2S bus.
This I2S to PCM converter board was developed exactly for this purpose under the requirement of audiophiles. »
They also working on some multibit dac core board and I/V, so i think at this end this will become a complete dac 
However, they clearly say that for optimal quality, we need to bypass the digital filter (or use nos) of our dac with a better software resampler. it seems we have a very good resampler in linux with sox that can easily work with mpd :
http://soundcheck-audio.blogspot.fr/2011/04/tt-resampling.html
So, could we use the pi as a dsp to real-time resample ? With the Ian boards and multi-bit dac, you can send 32/384khz (8x). However some modern usb dac don’t support this, it seems to come from a limitation of the usb inferface, some usb board has update recently their firmware (waveio do it in september). However it’s still profitable for owner of nos dac (or owner of dac where you can bypass the digital filters) that want to have a better resampler than integrate circuit or dsp.
So the question is : the 700 mhz of the pi is enough for this kind of resampling with sox ? Their is also the limiations of the i2s alsa driver, that seems limited at 24bit/(96 or 192?).
