[sdiy] that darned record module i keep obsessing about

[rsdio at audiobanshee.com]

I phrased my reply poorly.

The MP3 part of your suggestion would actually be more "difficult" than the original problem, both in terms of the programming needed and the platform required. MP3 decoding involves frequency domain calculations that might be too much for a lot of the appropriate processors out there, and there are potential licensing issues with the code due to patents. The ARM in the Raspberry Pi is a processor that's designed with enough power to run a full operating system. Many processors that would actually be used in a digital recorder/player without DSP couldn't hope to run linux, or even decode MP3 files into a digital stream for a DAC. No sense starting with a system that's way overkill.

A WAV player would truly be a subset of the original idea that would be easier as a starting point. No processing is needed at all on a WAV file - the CPU can just shuttle data from the file to the DAC (later, from the ADC to the file) without any calculations. If you start with the minimum requirements of Serial Digital communications (TDM, etc.) for the DAC (and ADC) and an external memory bus, then there are a lot of inexpensive chips available that don't have complex BGA packages like the typical ARM. There might even be a PIC in a DIP package that could do this.

I do like your suggestion to start small. It's possible to just buy an Evaluation Board from a CPU maker and start programming before getting into schematic design and layout.

Things like the XMOS USB Audio DJ Kit (XR-USB-AUDIO-2.0-4C) would allow basic 2-channel audio input and output without any initial circuit design. Starting with playback might be simpler, then switch to recording and playback. Admittedly, the XMOS is not a "normal" processor because of the multi-core programming model, but they do have a 48-pin TQFP package that's not too unfriendly to beginners.

But there's probably something from ATMEL or Microchip that would be even easier. It would be best to pick one with an evaluation platform that already includes audio.

Brian Willoughby
Sound Consulting


On Aug 17, 2014, at 12:29 AM, Andrew Simper wrote:
> On 17 August 2014 11:22,  <rsdio at audiobanshee.com> wrote:
>> An MP3 player would still have to store the file somewhere in order to play it back. Whether SD card or Flash, there's still a file system with audio files. By the time you get an MP3 player working, you might as well do WAV playback.
>> 
>> But I think Henry's original idea was to capture modular moments by allowing you to record when you hear something interesting going on. An MP3 player would be a different tool than that.
>> 
>> Brian
> 
> Not sure if you understood my point, perhaps you just skimming what I
> said? I know what he wants to do, my point is that an mp3 player is
> actually an "easier" thing to do that what he proposes, which I said
> to try and put things in perspective of the work / tech involved.
> 
> 
>> On Aug 16, 2014, at 6:54 PM, Andrew Simper wrote:
>>> Just remember that an mp3 player could actually be considered an
>>> easier thing to make by your criteria, since that only has to play
>>> back a signal, not record it and then store it as well!
>>> 
>>> Have you checked into the Raspberry Pi? They have SD card and ADC DAC
>>> adon cards eg: http://www.electronicsweekly.com/news/design/embedded-systems/132705-2014-03/
>>> 
>>> Andy
>>> 
>>> On 16 August 2014 23:42, Henry Birdseye <henry.birdseye at gmail.com> wrote:
>>>> Okay,
>>>> 
>>>> I've been way overthinking this idea. How much does the viability go up if
>>>> it's 2 analog 10v p-p signal going into level control, a place to plug a
>>>> flash card and a big red button that starts and stop recording directly to
>>>> the card. nothing else. no dsp, no programming, just addac and data
>>>> transfer.
>>>> 
>>>> Sound better?
>>>> 
>>>> hb
>> 
>