I have a slightly crazy project, which I would like input on - especially if anyone has tried this already. I am using a Linux setup on my main computer, which also passes internet service on to the LAN, with IP addresses given by avahi. The stereo is in another room, with audio duties being provided by an Airport Express, using raop_play as the necessary software to stream audio. This works pretty well on the whole, and since I am unable to get a Squeezebox down here in Brazil it is probably the best option I have available commercially for connecting the stereo to my computer.
But this is diy, right? Here is the idea. The world is full of laptops that no longer have working batteries, or don't run the latest version of windows, or whatever. I am considering opening up such an old laptop and pulling off an I2S signal (probably from somewhere on the soundcard, if I can locate it...) to be sent to a DAC. The laptop needs to be able to run a minimal linux kernel (I plan on using gentoo, although it makes little difference) but doesn't need to store large quantities of music at all - just to pass on what it receives over the LAN. Of course, all this is possible using a USB output, but it seems like it would be better to send the I2S directly to the DAC chip rather than to convert to USB and then back to I2S before DA conversion.... The main advantage would be to have flexibility (and diy fun!) in the DAC itself, having the possibilty of 24bit audio and so forth. Of course, it would have to be a pretty old and worthless laptop, because i may well kill it trying to pull off an I2S signal...
Has anyone tried this? It seems unlikely I am the first to think of this, so if anyone has experience or ideas I'd be very happy to hear about them.
But this is diy, right? Here is the idea. The world is full of laptops that no longer have working batteries, or don't run the latest version of windows, or whatever. I am considering opening up such an old laptop and pulling off an I2S signal (probably from somewhere on the soundcard, if I can locate it...) to be sent to a DAC. The laptop needs to be able to run a minimal linux kernel (I plan on using gentoo, although it makes little difference) but doesn't need to store large quantities of music at all - just to pass on what it receives over the LAN. Of course, all this is possible using a USB output, but it seems like it would be better to send the I2S directly to the DAC chip rather than to convert to USB and then back to I2S before DA conversion.... The main advantage would be to have flexibility (and diy fun!) in the DAC itself, having the possibilty of 24bit audio and so forth. Of course, it would have to be a pretty old and worthless laptop, because i may well kill it trying to pull off an I2S signal...
Has anyone tried this? It seems unlikely I am the first to think of this, so if anyone has experience or ideas I'd be very happy to hear about them.
I do not think laptops internals offer a significantly cleaner environment than desktops. Noise on their analog outputs is basically comparable to that of integrated sound cards on desktop motherboards.
An old NTB will feature codec with AC97 links, a newer NTB will have a codec linked to the south bridge via Intel HDA protocol. None of those are directly I2S compatible.
An old NTB will feature codec with AC97 links, a newer NTB will have a codec linked to the south bridge via Intel HDA protocol. None of those are directly I2S compatible.
Wow. I woke up and found all these responses...
OK. If there is no DA chip then my original idea is dead in the water.... At least using the USB output should be possible, right? (Although much less appealing from a diy point of view) Would your remarks about a noisy environment apply here also? What about jitter?
Yes, I really liked the look of this. The problem is that importing one into Brazil is expensive. (70% import taxes on top of the value of the board *and* postage/packing...) I had the idea of using an old laptop while fishing around for a cheaper alternative.
Yes, could you explain further? Perhaps this is the cheaper alternative I was looking for....
Thanks
Nigel
tritosine said:those laptops have codec chipsdead: ) no seperate DA, you could only tap i2s before toslink transmitter, then you have something like 5-10 ns jitter embedded in spdif signal (forget bout 16bit) coming out of some noisy enviroment.
Not worth considering.
OK. If there is no DA chip then my original idea is dead in the water.... At least using the USB output should be possible, right? (Although much less appealing from a diy point of view) Would your remarks about a noisy environment apply here also? What about jitter?
Scrappydoo said:
Yes, I really liked the look of this. The problem is that importing one into Brazil is expensive. (70% import taxes on top of the value of the board *and* postage/packing...) I had the idea of using an old laptop while fishing around for a cheaper alternative.
tritosine said:
Scrappydoo said:
Yes, could you explain further? Perhaps this is the cheaper alternative I was looking for....
Thanks
Nigel
phofman said:
Well, I wasn't planning on using the analogue outputs. (In my original idea, now apparently dead, I was planning on pulling a digital I2S signal out of the box). What would you think of using the usb output, if I had an appropriate USB DAC, or a USB-I2S converter or something? (As I mentioned above this is less appealing from a diy point of view...)
As a further query, what would be the principal offender for generating noise? The PSU? Hard drive? Perhaps one could reduce noise by pulling out or deactivating parts not needed for this application. (Which is pretty simple compared to normal laptop business, it seems to me...)
Thanks
Nigel
Cool board - would like to see someone do an audio project with it.
Back to the topic. If you can't pull I2S off a laptop board, that's too bad. Would be a nice hack. The only easy way I know for USB to I2S is one of the BurrBrown USB DAC chips. Pretty simple and cheap. Can be USB bus powered. Limited to 32, 44.1, 48 Khz/ 16 bits.
Have you looked at any of the mini-itx boards? Maybe they can do what you want within budget?
Back to the topic. If you can't pull I2S off a laptop board, that's too bad. Would be a nice hack. The only easy way I know for USB to I2S is one of the BurrBrown USB DAC chips. Pretty simple and cheap. Can be USB bus powered. Limited to 32, 44.1, 48 Khz/ 16 bits.
Have you looked at any of the mini-itx boards? Maybe they can do what you want within budget?
Sorry about the long delay in replying. I am learning the hard way that old laptops may (and usually do) have unexpected things wrong with them....
At this point I have given up on the original laptop hack idea - apart from the problems that people explained above, I am finding that any laptop cheap enough to make the project attractive on cost grounds probably has too many problems to make it attractive in terms of time invested.
So here are a couple of remarks on replies from above.
This looks really nice. I am trying to convince myself that food/clothes and so forth for the kids aren't really so important and I really *need* one of these....
I know there's a wiki, which I plan on reading in detail, but has anyone here bought one and used it as I would like to, as the first half of an ethernet DAC? Do you like it?
I have built an Alien DAC kit, which uses one of the BB chips, and is fine as far as it goes (which is already a long way, if you ask me) but the real heart of the idea was to avoid transforming an I2S stream to USB and then back again...
Actually one of the mini- or pico-itx boards was top of my list until I saw the beagle board, but all of the above have the problem of import taxes. The avr32 board above looks like a more cost-effective option. Again, if anyone has experience I'd love to hear about it. (A related non-audio question is how do people prefer to set up an interface with the board?)
Cheers
Nigel
At this point I have given up on the original laptop hack idea - apart from the problems that people explained above, I am finding that any laptop cheap enough to make the project attractive on cost grounds probably has too many problems to make it attractive in terms of time invested.
So here are a couple of remarks on replies from above.
panomaniac said:
This looks really nice. I am trying to convince myself that food/clothes and so forth for the kids aren't really so important and I really *need* one of these....
I know there's a wiki, which I plan on reading in detail, but has anyone here bought one and used it as I would like to, as the first half of an ethernet DAC? Do you like it?
panomaniac said:
I have built an Alien DAC kit, which uses one of the BB chips, and is fine as far as it goes (which is already a long way, if you ask me) but the real heart of the idea was to avoid transforming an I2S stream to USB and then back again...
Actually one of the mini- or pico-itx boards was top of my list until I saw the beagle board, but all of the above have the problem of import taxes. The avr32 board above looks like a more cost-effective option. Again, if anyone has experience I'd love to hear about it. (A related non-audio question is how do people prefer to set up an interface with the board?)
Cheers
Nigel
Inside a laptop you'll probably see AC97, not I2S, connecting the audio codec.
With a bit of creativity (using a dsPIC or something) you might be able to grab the AC97 bus, pull out the primary audio signals and convert them to I2S. However, AC'97 runs at a fixed 48KHz sample rate and you're at the mercy of the soundcard driver or southbridge chipset and how well it SRC's its audio to that rate.
I'd go with a USB audio solution. Easier and a whole lot more people have done it that way.
With a bit of creativity (using a dsPIC or something) you might be able to grab the AC97 bus, pull out the primary audio signals and convert them to I2S. However, AC'97 runs at a fixed 48KHz sample rate and you're at the mercy of the soundcard driver or southbridge chipset and how well it SRC's its audio to that rate.
I'd go with a USB audio solution. Easier and a whole lot more people have done it that way.
Hi Guys,
Sorry, but it took a while for me to notice this old thread had been revived...
While 192kHz would be nice, I'd still be pretty happy with 96kHz. In any event, do you have another suggestion for 192kHz at a reasonable price? When time and money permit I'd like to go back to these ideas...
As I think I mentioned above somewhere, I've dropped the idea of pulling I2S out of an old laptop as being more trouble than it's worth - in part for reasons similar to those you are giving. When you mention a "USB solution" are you thinking of the TI PCM270* chips? Or something more sophisticated?
I've done a couple of circuits with the PCM2707 (and an Alien DAC with the PCM2702) but the idea of the project was to avoid converting I2S -> USB -> I2S. The board mentioned above should allow an input from the ethernet and a direct output to a I2S DAC such as PCM1793 or PCM1794. without the intermediate USB stage. Or that was the idea, anyway...
For the time being these ideas have taken a back seat to other projects (and in fact work pressure hasn't allowed me to do much diy lately) but I am still giving it some thought, and I'd be interested to read any posts people might have.
Cheers
Nigel
Sorry, but it took a while for me to notice this old thread had been revived...
While 192kHz would be nice, I'd still be pretty happy with 96kHz. In any event, do you have another suggestion for 192kHz at a reasonable price? When time and money permit I'd like to go back to these ideas...
As I think I mentioned above somewhere, I've dropped the idea of pulling I2S out of an old laptop as being more trouble than it's worth - in part for reasons similar to those you are giving. When you mention a "USB solution" are you thinking of the TI PCM270* chips? Or something more sophisticated?
I've done a couple of circuits with the PCM2707 (and an Alien DAC with the PCM2702) but the idea of the project was to avoid converting I2S -> USB -> I2S. The board mentioned above should allow an input from the ethernet and a direct output to a I2S DAC such as PCM1793 or PCM1794. without the intermediate USB stage. Or that was the idea, anyway...
For the time being these ideas have taken a back seat to other projects (and in fact work pressure hasn't allowed me to do much diy lately) but I am still giving it some thought, and I'd be interested to read any posts people might have.
Cheers
Nigel
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