[sdiy] newbie question Can a simple PIC16F628A be used as an audio filter trigger like a light organ

[rsdio at audiobanshee.com]

On Feb 24, 2016, at 7:35 AM, Rob <roomberg at ptd.net> wrote:
> 1. Can anyone recommend a particular DSP  chips to play with to make filters?
I'd recommend the TMS320C5505. Texas Instruments has an eZdsp USB Stick Development Tool for $49

http://www.ti.com/tool/tmdx5505ezdsp

This has audio conversion built in, and is totally powered by USB. There's some kind of edge connector that might allow you to easily connect your LED outputs without designing a whole PCB.

> Is there anything the hobbyist  can use that is not strictly assembler?
I have written C55xx code that is entirely in C. The FFT and other DSP subroutines are in assembler, but are provided by Texas Instruments so you don't have to edit them to get them to work. There are C calling conventions that allow you to use the provided assembly without learning how to write assembly yourself. They also have an open source forum for the assembly tools so that you can share with other developers who might know more about TMS320 assembly.


> 2. why not use 6,7,8 kHz in the same octave?
> I thought the whole idea of using digital chips would give more granularity.
I didn't mean to imply that it wouldn't work at all. It's more of a creative choice. I was predicting that it might not work as well as you hope, but I could easily be wrong. There's certainly no reason not to try your idea.

A very simple 16-point or 32-point FFT would give you bins that are spaced by 1 kHz, especially with a low audio sample rate, and you could see whether it looks good. If it doesn't look interesting, then you can increase the number of bins and aim for logarithmic / octave spacing of the bands by combining multiple bins as appropriate.

I don't know whether the CODEC chips on the TMDX5506EZDSP can run at 22.05 kHz or 20 kHz, but that would give you plenty of processing power since you don't need high fidelity audio processing for a light organ. Of course, it would probably work at standard rates like 44.1 kHz, too.

Brian