[opus] [Opus][RFC][FFT][Fixed-Point][NEON] NEON-Optimize

[Phil Wang]

Hi Jean-Marc,

I have implemented fixed-point FFT with 32-bit twiddles. Now I want to
evaluate the accuracy, what method does Opus use?
I use function implemented inside Ne10 to calculate SNR. Any comment?

|  size |    SNR (dB)  |
|   16  | 82.558587 |
|   32  | 83.530298 |
|   60  | 80.292433 |
|   64  | 82.752950 |
| 120  | 79.625077 |
| 128  | 83.091260 |
| 240  | 79.555263 |
| 256  | 82.470671 |
| 480  | 79.741435 |
| 512  | 82.675800 |
| 900  | 79.098034 |
| 960  | 79.737709 |

If Opus are using other method to evaluate the accuracy, can you kindly show
me the path?

Best Regards,
Phil Wang

> -----Original Message-----
> From: Jean-Marc Valin [mailto:jmvalin at jmvalin.ca]
> Sent: Tuesday, December 30, 2014 3:30 AM
> To: Phil Wang; opus at xiph.org; Timothy B. Terriberry (tterribe at xiph.org)
> Cc: Zhongwei Yao; Yang Zhang; Zhou (Joe) Yu; Steve Bannister
> Subject: Re: [opus] [Opus][RFC][FFT][Fixed-Point][NEON] NEON-Optimize
> 
> On 28/12/14 11:04 PM, Phil Wang wrote:
> > It requires some extra effort if twiddles and input/output have
> > different bit width.  Since Opus uses int32 for twiddles, we are going
> > to do the same thing.
> 
> Actually, the existing Opus code has 16-bit twiddles, mostly because it
makes
> it possible to use smulwb on ARMv5E. That being said, I agree that for
Neon it
> makes sense to use 32-bit twiddles since there's no 16x32 multiplier.
> 
> Cheers,
> 
> 	Jean-Marc
> 
> >
> >
> > Thanks,
> >
> > Phil Wang
> >
> >
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