pt2399 noise. solution?!

[kothoma]

The main reason I was interested was that I've been hoping to find a DSP or MCU with an attached CODEC just to make the whole hardware side of doing digital DIY pedals simpler.

Now that would be great!

Well, looking more into the Raspberry Pi I stumbled upon this little I²S guy:
http://eu.mouser.com/Search/Refine.aspx?Keyword=wm8731
http://www.wolfsonmicro.com/products/audio_hubs/WM8731/
http://www.wolfsonmicro.com/documents/uploads/data_sheets/en/WM8731.pdf (Have a look at p60.)

http://www.mikroe.com/add-on-boards/audio-voice/audio-codec-proto/ (€15.20 at Mouser)
[Edit: forgot to mention: this one uses for input only the mono mic pin, the stereo line in pins are not used ]

And indeed someone tested it sucessfully:
http://blog.koalo.de/2013/05/i2s-support-for-raspberry-pi.html

Just add a little buffer/booster to the circuit and plug in your guitar?

[RobA]

Thanks for the links to the projects. They could be very useful. I've got some of the WM8731 and some Cirrus Logic CS4270 as well on DIP adapter boards and they both work well for getting audio into MCU's, Raspberry Pis, etc. but that little breakout board looks like it could be really handy for experimenting with. If I can ever get my hands on a BeagleBone Black, I'll probably end up using either of these two CODEC's to test it with. The WM8731 is also used in this shield for the Arduino http://www.openmusiclabs.com/projects/codec-shield/. They've got the schematic available for the complete shield as well.

I'd still like a complete single chip solution for smaller digital projects. I've been wondering more-and-more if the custom chip in the Digitech stuff is an FPGA and I'm thinking of going down that route. Of course, that's a whole new world of programming and interfacing I'll have to learn...

[kothoma]

... They've got the schematic available for the complete shield as well.

Right. Found it in their wiki. Thanks for this hint!

I'd still like a complete single chip solution for smaller digital projects.

Strange that there wouldn't be such a thing. Indeed it would be great to have and build a compact generic platform with.
For now I'll try my luck with the RasPi and a USB audio interface (which can drive you crazy).

[RobA]

I haven't tried using USB audio into the RasPi yet. In general though, I think using USB audio into various of the devices opens up a whole range of devices to use as processors. On the input and ADC side of things, Atmel and XMOS have some pretty slick chips to help with the USB audio connections and some processing and interface to pots and switches and such.

[kothoma]

[...] Atmel and XMOS have some pretty slick chips to help with the USB audio connections [...]

Providing a USB host (or client)?

[RobA]

Either side I think, but I've mainly looked at it for the client side. I've been thinking of doing a "pedal" that would let me connect to an iPad, Android (if they ever fix the audio/RT issues), BeagleBones, etc. for the digital processing and I've kinda settled on doing it as a USB audio device to get the universal connection. 

[kothoma]

[...] Android (if they ever fix the audio/RT issues) [...]

I think I read some days ago that Samsung succeeded in adapting Jack(?) to Android. Sorry, can't find that link any more.

[RobA]

[...] Android (if they ever fix the audio/RT issues) [...]

I think I read some days ago that Samsung succeeded in adapting Jack(?) to Android. Sorry, can't find that link any more.

Interesting. I couldn't find anything on the JACK site. I'll do some more searching and see what I can find. Though, I'm not sure it would help with the latency anyway since the issue seems to be in the kernel and the basic design of Android. Maybe 4.4 will help with its new model, but I'm really not holding out much hope. At this point, I'm really hoping that some of the other alternative tablet OSes will be usable for audio applications.

[kothoma]

http://jack-audio.10948.n7.nabble.com/Jack-Devel-JACK2-for-Android-td17329.html
[http://global.samsungtomorrow.com/?p=29466]
http://developer.samsung.com/samsung-mobile-sdk#professional-audio

Haven't dug any deeper though.

[RobA]

http://jack-audio.10948.n7.nabble.com/Jack-Devel-JACK2-for-Android-td17329.html
http://global.samsungtomorrow.com/?p=29466

Haven't dug any deeper though.

Thanks for the links. It looks like the JACK implementation is very limited to just a couple of Samsung devices. And, even on those it looks like the source is modded so that even the MIDI implementation isn't low latency. I don't know for sure though. I did some web searching based on the info in the links though and the results still don't look good for KitKat at this point. I guess that might change in the future. I guess we'll have to wait to see some reports from users in the wild to know how well each of these work.

Meanwhile, I still can't get my hands on the new BeagleBone because they are sold out everywhere. Argh, they look so promising.

[kothoma]

[...] It looks like the JACK implementation is very limited to just a couple of Samsung devices. [...]

That's my impression too. I'm not sure about how much is open sourced here and what is proprietary.
But it's good to see that someone works on that ill-designed Android sound architecture.
On the other hand I never understood why anyone would need Android (in the form of a Java/Dalvik VM) on top of Linux in the first place.

[RobA]

[...] It looks like the JACK implementation is very limited to just a couple of Samsung devices. [...]

That's my impression too. I'm not sure about how much is open sourced here and what is proprietary.
But it's good to see that someone works on that ill-designed Android sound architecture.
On the other hand I never understood why anyone would need Android (in the form of a Java/Dalvik VM) on top of Linux in the first place.

From what I saw on one of the blogs, Samsung have put the source in their open source repository and people have pulled it. But, it does sound like it depends on specific hardware details. That makes sense though since my impression is that the audio latency problems are due to a combination of hardware and software.

I agree completely about the Android on top of Linux thing. It'll be great once the truly open Linux based devices gain some traction. We really can't be too far off from a Raspberry Pi tablet.

[kothoma]

[...] it does sound like it depends on specific hardware details. That makes sense though since my impression is that the audio latency problems are due to a combination of hardware and software. [...]

Yeah, that may very well be.

[kothoma]

[...] the new BeagleBone [...]

BeagleBone Black?

http://www.ebay.de/itm/321268837618

[RobA]

Yeah, that looks like it. I'm not sure what the price point is supposed to be in the EU with VAT and all. The US list is 45 I think. Sparkfun is nearby to me and is supposed to have them back in in about a week. That gives me a little bit of time still before I have to make up my mind if I want to go that way or try FPGA's first.