Block Floating point FFT or 32 bits precision FFT ?

Hello !

Sorry, this is my second question in two days .. 
I'd like to know if someone tried this two algorithms : Block Floating
point FFT and 32 bits (double precision) FFT..
Which gives the better result ?

Thank you for your advice..
	

Since you cc'd the C54x group, I assume you mean 16-bit block-floating
point
(i.e fixed point with a single exponent for the entire block) vs. 32-bit
pure fixed-point (i.e. double-precision for a C54x). Also assuming 16-bit
inputs and outputs in either case. Well, I have done the 16-bit
block-floating-point in C for a real-valued 2048-sample FFT, and got better
than 55 dB S/N in most cases, roughly a three-bit improvement over 16-bit
fixed-point. The implementation included rounding the butterfly results, not
just truncating, which helps a lot in accuracy but slows things down a
little (at least in C).

I believe a 32-bit fixed-point implementation ought to have much better
accuracy, even without rounding, but will be a lot slower, of course. In my
case, the CPU's L1 cache is too small for the block size, so the data
references all miss. With 32-bit values, everything is at least twice as
slow, maybe 4x for the multiplies. Admittedly, the block-floating-point
approach takes some overhead, but not that much.

Mark Egler
Analogic Corp.

> -----Original Message-----
> From: Curl [mailto:curl@curl...]
> Sent: Wed, December 05, 2001 5:48 AM
> To: audiodsp@audi...
> Cc: c54x@c54x...
> Subject: [audiodsp] Block Floating point FFT or 32 bits 
> precision FFT ?
> 
> 
> Hello !
> 
> Sorry, this is my second question in two days .. 
> I'd like to know if someone tried this two algorithms : Block 
> Floating point FFT and 32 bits (double precision) FFT..
> Which gives the better result ?
> 
> Thank you for your advice..
> 
> 
> 
> 
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