Truncated match.
PICList
Thread
'FFT with 16C84? Rather not'
1997\02\10@201509
by
Kalle Pihlajasaari

Hi Hendrik & David,
> > We are thinking of building a simple audiospectrumanalyzer.
> > The output would consist of a LEDmatrix (7 bars, 8 LEDs / bar).
>
> The short answer is no. The '84 does not have anywhere near enough
> resources to perform realtime FTs. Even 'touchtone' 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 XR1091 .. XR1097.
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_OUTkalleTakeThisOuTip.co.za http://www.ip.co.za/ip
Interface Products P O Box 15775, DOORNFONTEIN, 2028, South Africa
+ 27 (11) 4027750 Fax: 4027751 http://www.ip.co.za/people/kalle
DonTronics, Silicon Studio and Wirz Electronics uP Product Dealer
1997\02\10@225347
by
Dmitry Kiryashov

Kalle Pihlajasaari wrote:
>
> Hi Hendrik & David,
>
> > > We are thinking of building a simple audiospectrumanalyzer.
> > > The output would consist of a LEDmatrix (7 bars, 8 LEDs / bar).
> >
> > The short answer is no. The '84 does not have anywhere near enough
> > resources to perform realtime FTs. Even 'touchtone' 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..n1] SIN(Xi)*Y(INPUTi) ;
A2(k) = Sum [i=0..n1] COS(Xi)*Y(INPUTi) ;
[i=0..n1] > 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..n1] SIN(Xi+pi/4)*Y(INPUTi) ;
A4(k) = Sum [i=0..n1] 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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