Free/Libre wireless audio systems

[taylor]

I've got too many ideas to do on my own, so I want to share them with anyone who would like to help me explore the idea and design hardware for production. One big category of interesting projects is audio. I have several ideas here, but most can be done with one simple shield.

Flutter Free/Libre wireless audio system.

What is it?

A shield for Flutter with a digital audio CODEC that supports stereo audio input and output at headphone levels, with a selection of amplifiers to go with it.

Why make it?

Flutter supports data rates up to 1Mbps with sufficient range for home audio (tens of meters) and several hundred meters at something like 300kbps. This is plenty of speed for a high quality digital audio system including a very high end audiophile system for the home. At lower data rates, users could use the audio system as a digital intercom or walkie-talkie.

Additionally, home audio systems tend to be expensive and are often focused on locking users to other services. A Free/Libre hardware system will meet your needs without exploitative pricing or compromises on features.

Desired features

Support for Audiophile-levels of quality. Not a really expensive CODEC/DAC (with audio the sky tends to be the limit) but not the cheapest or easiest to support CODEC/DAC either. Sparkfun for example has some published open source designs we could borrow from, but we should not select those chips simply because they already exist. Effort should be made to discuss DAC options and choose the most appropriate chip, based on requirements determined by discussion.

Should support stereo audio input and output.

At least one amplifier should be made. For my needs I am thinking of a medium power amplifier like 15w RMS 30W peak per channel. Basically I want to clone the audioengine A2 speakers.
http://audioengineusa.com/Store/Powered-Speaker-Systems/A2-plus-W-Powered-Desktop-Speakers#B

Design stage: concept

The wireless audio system is just a concept. An appropriate CODEC needs to be selected and at least a medium power amplifier sufficient to drive something like an Audioengine A2-style speaker would

TODO

Evaluate CODEC chips.
Evaluate Amplifier options.
Evaluate speaker options.
Evaluate microphone options.
Make final decisions on chips for v1.
Design v1 and order hardware.
Develop software.
Test and evaluate v1 hardware.

Contributors

@taylor
(Anyone want to help? Anyone know anything about audio and/or PCB design?)

[taylor]

Possible CODEC Chips

I searched on TI's website and found several interesting options, but they have a large matrix of choices. I don't know of other possible manufacturers, but I'm partial to TI when in doubt.

http://www.ti.com/product/pcm3052a/description
http://www.ti.com/product/pcm3070/description

TI actually has a full end product reference design!
http://www.ti.com/solution/audio_dock_performance

They are using a similar radio too, so software and hardware suggestions should be there.

Whoa!

TI has a complete set of reference designs and a 55 page Audio Design guide!
http://www.ti.com/lit/sl/slyy013g/slyy013g.pdf

People keep telling me I need to talk to the reps at TI. They're a mile down the road. I should really do that... this give me ideas.

Anyway, anyone chime in with thoughts. I won't have time to tackle something like this for a few months.

[taylor]

Oh, the Audioengine A2's feature page says which DAC they use, and it's a TI part:
http://www.ti.com/product/pcm2704c

That one is USB which we can't use here, but we should try to find something with comparable specs.

[jet_flyer]

I can help with the PCB since that's what I'm taking classes for lol

[taylor]

That would be great! I haven't had more time to look at this, but I can design the schematic some day if you want to help with layout.

[robot54]

This topic is really interesting to me, so I'm going to jump in with questions and hopefully learn more.

I'm a little unsure of the different meanings of the word "codec". I know it means "code/decode", but I've heard it used in reference to both IC chips and software programs. Are the chips just a progression from software to hardware for efficiency purposes? Or do they provide other functionalities?

I came across the Opus audio format on Wikipedia and got really excited about it because it's been designed for streaming audio, and therefore has high quality with low bitrate requirements, like full range stereo in only 80kbps with ~25ms latency. More channels could easily be added with such low bandwidth, 5.1 surround! It is so new that I doubt a chip is available for it, but the reference implementation is open source and written in C. Is this something that could be ported to run on flutter? Is it even worth trying?

[taylor]

Hey, Opus looks really cool, it would definitely be valuable to have that working on Flutter!

By CODEC I mean a chip. They sell these lovely kits that take a serial byte stream of data in MP3, OGG, or WAV format and drive an audio amplifier with decoded sound. So hook one up via serial to Flutter and we don't have to try to decode in software. CODEC chips often can drive headphones without an amplifier, and they often also have microphone inputs to allow for Flutter walkie-talkies or intercoms.

I would love to make this board, just haven't had any time to spend on it!