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Author Topic: [REQ] DSPIC audio frequency shift.  (Read 2122 times)
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oldvan
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« on: September 04, 2009, 12:11:31 00:11 »

I'm working on an idea using a DSPIC30F6014 and would like to be able
to take the audio spectrum and shift it up by 20 KHz, such that what
was 20 Hz is now 20020Hz and what was 20000 Hz is now 40000 Hz.  At
the receiving end I'd like to reverse the process, moving everything
back to where it started out.  I'd like to be able to do this with
reasonable audio fidelity, perhaps 10-bit and 40K samples per second.

My biggest problem is I have no experience whatsoever with DSP
functions, so am in it up to my shoelaces head-first on this.

Could those with experience in this matter please let me know if my
plans are reasonable with the chip I have in mind, perhaps suggest
some code to get me started, and let me know some of the likely
pitfalls I'll encounter along the way.
« Last Edit: September 04, 2009, 12:55:23 00:55 by oldvan » Logged

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Prommer
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« Reply #1 on: September 04, 2009, 07:43:27 07:43 »

Hi, oldvan

The dsPIC30F is to slow for 80 KSample !  I have made my Frequency-Shifting Projekt with an FPGA (CYCLONE III).
On the web is an dsPIC-Sampleproject with F-Shifting but it work for 8 KSample. You neet an Hilbert-Filter, Multiplier and an NCO. The Hilbert must have 128 TAPS and more (256 TAPS) for optimal shifting (Bandpass i.e. the lower frequency part is critical fg = 0.005 * fs and 0.995 * fs). For more Information see SSB-Modulation !!!

best regards,

Prommer
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mitsos
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« Reply #2 on: September 04, 2009, 11:29:33 11:29 »

hi

instead of using digital means why you don't try analog ones, a multiplier is all you need and you can find in cheap fm stereo decoder chips.

regards
mitsos
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Mr. Spock
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« Reply #3 on: September 04, 2009, 12:32:12 12:32 »

Quote
instead of using digital means why you don't try analog ones, a multiplier is all you need and you can find in cheap fm stereo decoder chips.
That would be my solution too
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oldvan
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« Reply #4 on: September 05, 2009, 05:39:13 05:39 »

Perhaps the SA602 Double-balanced mixer and oscillator would be a good start
to an analog solution?

http://www.nxp.com/acrobat_download/datasheets/SA602A.pdf

Sometimes I get TOO carried away and try to do everything in the digital domain,
forgetting that KISS should be applied to all engineering problems.
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« Reply #5 on: September 05, 2009, 07:12:30 07:12 »

Yes, you can consider mitsos's idea as a KISS (keep it simple stupid) but simple and workability depends on design and preference, which varies individual to individual.
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