Hello Gregory,
In the link that you had provided, they are talking about the output pcm bit width and not about the fixed point data width. And some use floating point Math.
But I couldn't understand the logic why you have to stick to 4.28x1.31 alone. One thing I always thought was why it was necesssary that you should stick to 4.28 * 4.28 giving 4.28 itself. I can have some thing like 4.28 * 2.30 giving 5.27. After all your maximum pcm bit width at output is 24 and 27 fractional bits will give you the same effect as 28 fractional bits.
I had worked on a 3DSP processor some 3 years before but I don't remember any thing about it. How is the multiplier in 3DSP? I remember it as a 32 bit processor and I think there was a multiplication instruction which gives you the upper most 32 bit result of a 32 by 32 multiplication and is this the reson why you wants 4.28 by 1.31 multiplication?
One more thing accuracy test is to be done only for compl.bit in ISO test streams I believe.
Have a nice week end.
Cheers, Tony
-----Original Message----- From: Grigory A. [mailto:Ryhor@tut.by] Sent: Friday, March 26, 2004 1:49 PM To: Tony Francis Cc: mad-dev@lists.mars.org Subject: Re[4]: [mad-dev] III_requantize() accuracy
Hello Tony,
Friday, March 26, 2004, 2:53:52 PM, you wrote: TF> With 16 bit implementation on TI55x how much accuracy you got? And TF> how much accuracy improvement was there by changing the TF> multiplication into 4.28 by 1.31 instead of 4.28 by 4.28 used in MAD TF> decoder?
According to http://www.underbit.com/resources/mpeg/audio/compliance/
in best case limited accuracy is achieved. But in worst case ... rms still C*10^-4 but C - is bigger than limited accuracy require.
4.28x1.31 - I just have to use this one :) This is 3DSP hardware dependent - in another case - like 4.28x4.28 I need to do additional actions... So almost in all places decoder use constants less than 1.0 Only in synthesis part some of them are bigger than 1. But now I am working under synthesis and I am looking in way where constant which are bigger than 1 will be split on 2 part.
After I finish decoder we can measure accuracy :).