At 03:43 PM 9/18/99 -0300, Silvio wrote:
>I'm looking for a simple FFT routine for audio analisis (spectrum) that
>runs on
>low end PICs like the 16x84.
>The device have an ADC, and I need to separate the audio in 10, 7 or
>even 5 bands,
>to display it on a LCD screen or fluorescent tube, along with the signal
>intensity.
>I've seen a program that do 128 bands, and generates video, but it's too
>much for me...
>My application doesn't need to be very accurate, so any simple approach
>would work.

Another thought:

A simple approach to this limited problem is to use the same method used in
cheap spectrophotometers.

You set a collection 2-nd order notch filters for each of the bands required.

If the notch filters are implemented by infinite impulse response digital
filters, then only addition and multiplication are required. I would
recommend 16-bit addition to maintain accuracy and stability. Truncate to
8-bits at the end of the calculations.

Hopefully the frequencies of interest are low enough that these
calculations can be performed real-time!  My guess is that you'd need
hardware multiplies to keep up with even modest (1 kHz) audio.

================================================================
Robert A. LaBudde, PhD, PAS, Dpl. ACAFS  e-mail: ral@lcfltd.com
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