[OpenTRV-dev] Audio/FFT thoughts

[Mike Stirling]

What are you planning on doing in the frequency domain? If you have already filtered to 4 kHz as part of your decimation step then why not just integrate the square of your 64 samples to give you an indication of voice band power?

Mike
 
----------------original message-----------------
From: "Damon Hart-Davis" EMAIL ADDRESS HIDDEN 
To: "Closed list for developer discussions" EMAIL ADDRESS HIDDEN 
Date: Tue, 11 Jun 2013 08:40:30 +0100
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> Hi,
> 
> Some initial thoughts on audio occupancy detection with the ATmega, listening 
> out for voice (of a human or their radio/TV being on). I have done no feasibility 
> testing yet.
> 
> My current plan is to (~8-bit) sample with the ADC at 16kHz, in bursts of about 8ms 
> (between RTC ticks), using a simple exponential filter to reduce to 8kHz 
> samples. Take 64 samples which should allow me to examine frequencies in the 4kHz 
> to 500Hz band which probably covers most of "voice".
> 
> 1) I think that I can probably achieve this sampling rate even at 1MHz CPU clock 
> (default Arduino ADC sample rate at 16MHz CPU clock seems to be 9600Hz and I have a 
> prescaler to play with).
> 
> 2) I only intend to listen when I'm otherwise in danger of thinking the room 
> unoccupied, and in any case on a low duty cycle to save juice (eg one 8ms sample 
> block per minute or less for example).
> 
> 3) I have headroom to boost the CPU speed dynamically to 4MHz if I need to (I already 
> dynamically lower it when I need to).
> 
> What is hideously silly about this plan already?
> 
> Rgds
> 
> Damon
> 
> 
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