# maximum sequence size to compute FFT using BF535

Started by February 19, 2010
Hello
I am trying to compute DFT using FFT in BF535. My need is to compute DFT of about 1 megasamples(1 million points). But since I'm very new to the field and am using a DSP for the first time, I do not know whether this is possible. If it is possible using BF535, how much time does it take to do it?

Thank you.
On Fri, 19 Feb 2010, a...@gmail.com wrote:

> Hello
> I am trying to compute DFT using FFT in BF535. My need is to compute
>DFT of about 1 megasamples(1 million points). But since I'm very new to
>the field and am using a DSP for the first time, I do not know whether
>this is possible. If it is possible using BF535, how much time does it
>take to do it?

It's possible if you have enough ram. An FFT takes on the order of
N(logN) operations, so you are looking at 6 million operations. If each
"operation" is 10 clocks (it might be 100, I don't know) you are looking
at 60 to 600 million clocks or .1 to 1 second.

You'll need one hell of a big sine table too, but if you have enough ram
that only has to be set up once.

Patience, persistence, truth,
Dr. mike
Hi,
I have the same problem as well. I want to interpolate the DFT to get the DTFT and then take the appropriate frequency range to get the CTFT. To plot this on my PC (via USB) what software can I use. Is this option available in VisualDSP? In the VisualDSP manual, I read that, it takes the FFT before plotting the data. If it does, then one won't require the processor at all for computing DFT! Am I right in assuming the above thing(s)? Please guide me.
Thank you,
Hi Abhi,

Do you want to FFT of given array lenght 1 m?
or
u are interested in doing FFT of array length 1024.
( may be many 1024 lenght array will form a 1 m lenght data).

Based on the above we can think on for you.

Kind Regards
jk

----- Original Message -----
From: Mike Rosing
To: a...@gmail.com
Cc: a...
Sent: Friday, February 19, 2010 8:13 PM
Subject: Re: [adsp] maximum sequence size to compute FFT using BF535

On Fri, 19 Feb 2010, a...@gmail.com wrote:

> Hello
> I am trying to compute DFT using FFT in BF535. My need is to compute
>DFT of about 1 megasamples(1 million points). But since I'm very new to
>the field and am using a DSP for the first time, I do not know whether
>this is possible. If it is possible using BF535, how much time does it
>take to do it?

It's possible if you have enough ram. An FFT takes on the order of
N(logN) operations, so you are looking at 6 million operations. If each
"operation" is 10 clocks (it might be 100, I don't know) you are looking
at 60 to 600 million clocks or .1 to 1 second.

You'll need one hell of a big sine table too, but if you have enough ram
that only has to be set up once.

Patience, persistence, truth,
Dr. mike