Pc -> Dac, How ?

[peufeu]

Let's stop polluting the ESS thread, shall we ?

OK so :

- CD is dead
- DVD is dead
- SACD is dead
- Physical formats are dead anyway

This settled, and it being pretty obvious that FLAC stored on RAID backed up twice will outlast the original CDs by a few centuries, while being more convenient, and cheaper, let's get to how to make it also sound better.

So how to connect some high quality DACs to a PC ?
(or a Mac, let's not be religious, it's the same hardware anyway)

We're aiming for high quality, so no time to lose with known-bad solutions, like :

- Clock recovered from anything except maybe a VCCXO and then only if Guido Tent blesses it
- ASRC
- Master clock not in DAC
- Digital volume control
- etc

Also it should support multichannel 24-192 because, why build something that is already obsolete ? I wouldn't consider digitizing my vinyls at 16 bits, thank you.

So, in order to implement this :



We can do :

- Slaved soundcard
- FireWire
- Ethernet
- Asynchronous/bulk USB

Slaved soundcard is pretty easy, master clock in DAC, encode it as SPDIF, send to soundcard, soundcard sends SPDIF back, decode, play. However it is a bit clumsy, since how do you switch sample rates ? use replaygain ? you don't...

FireWire.
Apart from the fact that FireWire is dead, it's nice... OK, it needs a powerful CPU in the device like an ARM7, and a few tens of thousands of lines of code of firmware, and it's immature technology, and you'll need 6 months to make it work, but it's cool, it's Apple after all.
Bottom Line : USB is cheaper and this is what matters. If you need to put an ARM7 @ 50 MHz in your peripheral to do what a 8051 could do if you used USB, you gotta have a really good justification for it, because you're getting fired by the bean counters. That is what is killing FW. Yes, FW is a better protocol. Does it do the so much better that it can add $100-$200 to the end product price ? Hm...

The DICE is nice but you need to sign a NDA, it's expensive, needs a 4 layer board, the firmware is complex, etc, etc.

Ethernet.
Ethernet is nice. I used Ethernet to stream audio data to a little FPGA board. however Ethernet has two drawbacks :
- It needs a powerful CPU in the device
- It has rather high and random latency

Needing a powerful CPU in the device is bad, because in order to implement custom oversampling filters, digital active crossover, multichannel, etc, you really need a FPGA, and there are no off the shelf boards on the market which combine Ethernet + A good CPU + a good FPGA + cheap.

Also a $50 Intel Atom mini-itx mobo with a USB DAC, linux and netjack will do ethernet audio streaming for cheaper than anything, and it will decode your divx, and it will have a 19" LCD for Amarok.

Someone posted the Ethernut link... OK, it's nice. Is it better and/or cheaper than a $50 intel atom mini-itx board ? No, and no. OK, you could use it for stereo 44.1k...

USB
USB is nice because it is simple. A $100 Nexys board from Digilent, some firmware, some verilog, and you get 45 MBytes/s of streaming data. I have yet to implement the DSP chain and then connect a DAC to it. This should follow shortly. I will be using bulk mode, so the clock is in the DAC. I have a working Python driver which can stream data and access device registers over USB.

Bottomline : it was much easier than Ethernet (which I did) and FireWire (which I dropped) and harder than slaving a soundcard, but so much better.

Of course a custom linux kernel ALSA driver will need to be implemented. Someone will probably do it... that might or might not be me... it's nor very hard. All testing can be done using a userspace driver written in Python. Easy.

When it's done (!) it will be opensource so you can try it.

[hifimaker]

I'm just starting to play around with the AD Blackfin and Sharc DSP's. Blackfin is interesting option as in input device. The Blackfin has an onboard MAC and requires an external PHY. Blackfin also supports USB.

The thinking is to leverage a Blackfin running ucLinux, which is already supported, to connect to ethernet and process and decode the packets onto the I2S outputs. The blackfin could also control DAC chips control pins as needed. Of course spdif and TOS could be added as an option if desired with little effort.

I'm also looking at the Blackfin driving the SHARC for room correction, digital crossover, etc.

-David

[Telstar]

Firewire is not dead at all, it's strongly used in pro devices. It's not diffused in consumer dacs because of the need for drivers.

[tritosine]

Peufeu , exactly why an ASRC is considered bad? Esp, since the best measuring audio dac ever has it right inside the package.

Also, you seem to forgot that the TI / BB chips have direct downsampling option, the data is not harmed by downsampling filter that way. This is a very diy friendly solution in fact. One downside is that once you want to pass it 192khz (precise "whatever-phase" SRC computed inside PC) with direct ds engaged, you have to use uncommon clock freq to make it pass 200ish khz, therefore the computers soundcard can not be slaved to it, but again , I can sync to my ADC-s clock then, who cares?

One thing I could use is a multichannel co-phase sampled ASRC thats not limited to 210ish khz max output freq, and can do agresive dithering above 100khz.

Telstar, DW80xxx , you seem to prefer vaporware as far i see

[Russ White]

I have often wondered why one could not simply utilize existing I/O on a little Atom (some similar cpu) mobo to spit out I2S.

[Telstar]

Originally posted by tritosine

Telstar, DW80xxx , you seem to prefer vaporware as far i see

Prism audio, Weiss enginering, RME, MOTU, just to name the most famous are vaporware to you?

paleeeeze!

[Telstar]

Originally posted by Russ White
I have often wondered why one could not simply utilize existing I/O on a little Atom (some similar cpu) mobo to spit out I2S.

i2s is not the manna.

ST is a better standard, if you're aiming for the best you should go for that.

Many tried and none succeeded to get either of these from a computer. If you can do it, i'll kindly go straight ST or i2s into my dac.

[Russ White]

Originally posted by Telstar

ST is a better standard, if you're aiming for the best you should go for that.

Excuse my ignorance. What is ST?

[tritosine]

Originally posted by Telstar


Prism audio, Weiss enginering, RME, MOTU, just to name the most famous are vaporware to you?

paleeeeze!

Apple considered ALLLLLLLLL regular PCI cards obsolete on earthhhhhh when switched to intelmac. As for firewire, same song, when apple quits, its over, those who were on the bandwagon , well they are forced to come up with an adapter solution

[Telstar]

Originally posted by Russ White


Excuse my ignorance. What is ST?

It's a glass optical standard introduced long ago by AT&T and used on a few transports-dacs combo in the past (i.e. audio synthesis dax, muse) and IMO still unsurpassed.

http://en.wikipedia.org/wiki/File:ST_connector.jpg