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'FFT with 16C84? Rather not'
1997\02\10@201509 by Kalle Pihlajasaari

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Hi Hendrik & David,

> > We are thinking of building a simple audio-spectrum-analyzer.
> > The output would consist of a LED-matrix (7 bars, 8 LEDs / bar).
>
> The short answer is no.  The '84 does not have anywhere near enough
> resources to perform real-time FTs.  Even 'touch-tone' decoding
> is a challenge.
>
> You are better off using 7 analogue band pass filters and sampling
> the output peaks.  This could be done with a MUX input ADC such as
> the PIC16C74, or an external unit such as NSC's ADC8017 (16 input).
>
> If this seems like too much hardware, then use a DSP such as TI's
> DSP320Cxxx series.  I think some have inbuilt ADCs.

The DSPs are a good engineering solution if you want to make it
flexible.  Analog Devices makes a Development systems for about
US$ 100 I think.

What I left Out from my previous posting on the EXAR parts was
the part numbers.  They are XR-1091  ..  XR-1097.

1092 Has 12 bands and the MUX 20 pin IC
1097 has 7 bands and the MUX and ADC with serial control 14 pin IC

The others have analog or matrix display outputs.

Cheers
--
Kalle Pihlajasaari   spam_OUTkalleTakeThisOuTspamip.co.za   http://www.ip.co.za/ip
Interface Products   P O Box 15775, DOORNFONTEIN, 2028, South Africa
+ 27 (11) 402-7750   Fax: 402-7751    http://www.ip.co.za/people/kalle

DonTronics, Silicon Studio and Wirz Electronics uP Product Dealer

1997\02\10@225347 by Dmitry Kiryashov

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Kalle Pihlajasaari wrote:
>
> Hi Hendrik & David,
>
> > > We are thinking of building a simple audio-spectrum-analyzer.
> > > The output would consist of a LED-matrix (7 bars, 8 LEDs / bar).
> >
> > The short answer is no.  The '84 does not have anywhere near enough
> > resources to perform real-time FTs.  Even 'touch-tone' decoding
> > is a challenge.
> >
> > You are better off using 7 analogue band pass filters and sampling
> > the output peaks.  This could be done with a MUX input ADC such as
> > the PIC16C74, or an external unit such as NSC's ADC8017 (16 input).
> >

I think another method than FFT should apply at practice
(in case of _simple_audio_spec_analyzer).

I have use corellation method to solve problem like that
Result of corellation may be used like FFT coeficients.
Each corellation coeff computed as:
A(k)=(A1(k))^2 + (A2(k)^2)
where
A1(k) = Sum [i=0..n-1] SIN(Xi)*Y(INPUTi) ;
A2(k) = Sum [i=0..n-1] COS(Xi)*Y(INPUTi) ;
[i=0..n-1] -> Xn = m*2*pi (full sine or cosine period
- to minimize corellation sum deviation);

To better result I calculate corellation with
SIN(X), SIN(X+pi/4), COS(X), COS(X+pi/4)
A(k)= (A1(k))^2 + (A2(k))^2 + (A3(k))^2 + (A4(k))^2
where
A3(k) = Sum [i=0..n-1] SIN(Xi+pi/4)*Y(INPUTi) ;
A4(k) = Sum [i=0..n-1] COS(Xi+pi/4)*Y(INPUTi) ;

(in second case deviation A(k) resulting from
initial phase of input signal much less)

WBR Dmitry.

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