Re: [Fwd: Re: code working on simulator but not on device?]

Dear Jeff
I did normalize and quantize the sos to Q15. But the thing I am not getting any difference in the filtered output of non quantized and quantized coefficients. I checked the pole zero plot in both the case and its the same.
Following are my calculations:

Fs = 48000;
HalfFs = Fs/2;
Wp = 6000/HalfFs;
Ws = 8600/HalfFs;
Rp = 3;
Rs = 20;
[n,Wn] = buttord(Wp,Ws,Rp,Rs)

n
6

Wn
0.2587

[b,a] = butter(n,Wn);

b
0.0012 0.0075 0.0187 0.0249 0.0187 0.0075 0.0012

a
1.0000 -2.8748 3.9031 -3.0192 1.3840 -0.3521 0.0386

sos
1.0000 2.0085 1.0085 1.0000 -0.8084 0.1756
1.0000 2.0000 1.0000 1.0000 -0.9087 0.3215
1.0000 1.9915 0.9915 1.0000 -1.1577 0.6836

g
0.0012
With above values and i/p as
X = [100, 200, 150, 345, 23, 678, 23, 567, 890, 46]
my output came :
R = filter(b,a,X)

R
Columns 1 through 8

0.1246 1.3546 6.9579 22.8703 54.7673 103.0378 160.8801 218.3556

Columns 9 through 10

268.7207 312.9030
Now I divided whole sos by 2.0085 (normalize) and multiplied by 32768 (for
> Q15) and then cal a and b:
sosnew=sos/2.0085

sosnew
0.4979 1.0000 0.5021 0.4979 -0.4025 0.0874
0.4979 0.9958 0.4979 0.4979 -0.4524 0.1601
0.4979 0.9915 0.4937 0.4979 -0.5764 0.3404

sosnew = sosnew*32768

sosnew
1.0e+004 *

1.6315 3.2768 1.6454 1.6315 -1.3188 0.2864
1.6315 3.2629 1.6315 1.6315 -1.4826 0.5246
1.6315 3.2491 1.6177 1.6315 -1.8888 1.1153

[b,a] = sos2tf(sosnew,g)
b
1.0e+011 *

0.0541 0.3245 0.8113 1.0818 0.8113 0.3245 0.0541

a
1.0e+013 *

0.4342 -1.2484 1.6949 -1.3111 0.6010 -0.1529 0.0168

and calculated filter on same data with these values:
R = filter(b,a,X)

R
Columns 1 through 8

0.1246 1.3546 6.9579 22.8703 54.7673 103.0378 160.8801 218.3556

Columns 9 through 10

268.7207 312.9030

So now you can see that, both the times R value is same. I dont understand why the values are not changing. Kindly provide your opinion.
Kinldy reply.
Thanking You
Megha Daga

Jeff Brower wrote: Megha-

After normalizing and changing to Q15, then print sos again. What does it
look like? If looks correct, then maybe sos2tf() does a normalization of
its own, and puts the values back again. In that case, maybe you have to
normalize and quantize b and a matrices.

-Jeff

> i just need to confirm what I am doing:
> As you suggested to normalize the data and then quantize. I tested it on
> matlab in the following manner:
> initially sos was:
> sos >
> 1.0000 2.0085 1.0085 1.0000 -0.8084 0.1756
> 1.0000 2.0000 1.0000 1.0000 -0.9087 0.3215
> 1.0000 1.9915 0.9915 1.0000 -1.1577 0.6836
> g >
> 0.0012
> With above values and i/p as
> X = [100, 200, 150, 345, 23, 678, 23, 567, 890, 46]
> my output came :
> R = filter(b,a,X)
>
> R >
> Columns 1 through 8
>
> 0.1246 1.3546 6.9579 22.8703 54.7673 103.0378 160.8801
> 218.3556
>
> Columns 9 through 10
>
> 268.7207 312.9030
> Now I divided whole sos by 2.0085 (normalize) and multiplied by 32768 (for
> Q15) and then cal a and b:
> [b,a] = sos2tf(sosnew,g)
> b >
> 1.0e+011 *
>
> 0.0541 0.3245 0.8113 1.0818 0.8113 0.3245 0.0541
> a >
> 1.0e+013 *
>
> 0.4342 -1.2484 1.6949 -1.3111 0.6010 -0.1529 0.0168
>
> and calculated filter on same data with these values:
> R = filter(b,a,X)
>
> R >
> Columns 1 through 8
>
> 0.1246 1.3546 6.9579 22.8703 54.7673 103.0378 160.8801
> 218.3556
>
> Columns 9 through 10
>
> 268.7207 312.9030
> and the result is same. Hence I dont see any effect by normalizing and
> then quantizing.
> I think this method should work.
> Jeff kindly correct me if I am going wrong anywhere. I also checked a
> random data on TO device and MATLAB and both give same output. Hence I
> guess, if this quantizing thing works on matlab, it should work on C5416.
> Kindly provide your suggestion. My filter is an IIR low pass filter with
> cut off at 6000Hz (for speech signal).
> Thanking You
> Megha Daga
>
> Jeff Brower wrote: Megha-
> wont the scaling of coefficients effect the filter response?
> Scaling all coefficients changes the overall filter gain, but the not the
> shape of the frequency response.
> -Jeff
> Jeff Brower wrote: Megha-
> Thanks for the reply. But I guess I need the format in Q15 to use it in
> the command iircas51. Even if I convert it to Q13, it wont work.
> Can you suggest a method so that I can quantize/normalize my whole data
> between 1 and -1. After that I can convert it into Q15 and I guess that
> should work.
> iircas51() uses 5 coefficients per biquad, so it makes no assumption that
> one coefficient = 1 (see iircas4 function). In that case, you can try
> dividing all coefficients by the magnitude of your largest coefficient.
> Call this a scale factor k. Then apply 1/k to final output before it goes
> to the AIC to allow correct overall gain for filter output. Note that you
> should *not* apply 1/k to y[n] values -- only to D/A output, which I think
> can be more than 16 bits on the DSK 5510 board.Hopefully your IIR filter
> can then work in Q15 without overflow. If not, then trying increasing
> k.-Jeff
> Jeff Brower wrote: Megha-> I had a query in Q
> format. I am using iircas51 for IIR filter. In that
>> the coefficient data type should be DATA thats defined as short. So my
>> query is its not necessary to use Q15 format. I can aswell use Q2.13
>> format. But jeff is there any function to convert float to Q2.13 as
>> there is for float to Q15.To convert floating-point coefficients to Q13,
>> multiply by 8192 (instead
> of 32768 for Q15).I.e. multiplier = 2 ^^ QThis assumes all of your
> coefficients are less than +/- 4.0-Jeff> Jeff Brower wrote: Megha- I had
> one question.
>> In functions like butter (for filters) we declare a variable Wn (the cut
>> off frequency). ex: [B,A] = BUTTER(N,Wn). In this Wn value is between 0
>> and 1, where 1 means half of sampling rate. What I am not understanding
>> is
>> where is it getting sample rate value from. I saw some codes and in that
>> the sample rate value is not declared before using the command. Directly
>> the command is used. Where is it getting sample rate value from?
>> What I understand is suppose I have to run that filter design on an AIC.
>> And AIC is set at some sampling rate ex 48KHz. Then the code is
>> understanding that sample rate and setting Wn accordingly. Kindly
>> correct
>> me if I am wrong.
>> If your actual sampling rate is 48 kHz, and you want lowpass Butterworth
>> filter with 2 kHz cutoff, then set Wn = 0.0833.
>> Digital filters don't "know" the actual analog sampling rate; they only
>> know the Z-plane unit circle, or 0 to 1 as you mention. In this example,
>> if you vary the sampling rate (reprogram the AIC) then the filter cutoff
>> is always 0.0833*fs/2.
>> -Jeff
>>
>> Jeff Brower wrote: Megha-
>> I tried getting more material on maxflat but I am not getting much. I am
>> not understanding what exactly SOS and G stand for.
>> If I want coeff for IIRCAS51 (cascaded IIR filter design with biquads
>> qith
>> 5 coefficients) I want 3 coeff for zero (numerator) and 2 for poles
>> (denominator). I am not getting how to get those. i am not understanding
>> what does what stand for.
>> Maxflat() is for Butterworth IIR filter design. It's one option -- you
>> also might want Chebyshev or elliptic design.Another MATLAB function for
>> converting direct-form transfer function to cascade of biquad sections
>> is
>> tf2sos(). Here are some pages that might give you some clues:
>> http://www.math.psu.edu/local_doc/matlab/toolbox/signal/tf2sos.html
>> http://www.ee.ic.ac.uk/pcheung/teaching/ee3_Study_Project/iir_lab2.pdf-Jeff
>> Jeff Brower wrote: Megha-
>> > This is in continuation to my previous mail. I also tried with a
>> breakpoint at my
>>> next statement after fltoq15. If I run that. It stops in between and
>>> gives the
>>> error:
>>> Trouble running Target CPU: Attempted write to ROM at Addr:0x00ffff,
>>> Page:0
>>> I guess it is because of the infinite loop thing. Kindly reply and
>>> suggest
>>> something.Waiting for your reply.Your code is trying to write somwhere
>>> in mem locations 0x8000-0xffff, which are
>> external Flash as you mentioned before. Writing directly to Flash area
>> won't work
>> (although there is a way, which involves a series of Flash chip-specific
>> commands).
>> You have to check the C code ptr and array address values just before
>> the
>> breakpoint
>> to see why they are not pointing at onchip or offchip SRAM.Also, did you
>> see the c55x group thread about IIR cascade fixed-point filters? I've
>> included a copy of the latest message below. If you're not subscribed to
>> the c55x
>> group, you should. C55xx devices are the next generation after C54xx --
>> both 16-bit
>> fixed-point.-Jeff
>> -------- Original Message --------
>> Subject: Re: [c55x] IIR filter coefficients in iircas5 dsplib
>> Date: Tue, 16 May 2006 08:37:25 +0200
>> From: Christian Narvaez
>> To: c... thanks Misan, thanks RK:
>> indeed this was the problem... I have successfully implemented the
>> filter now.CNnasim ahmed ha scritto:
>>> hi christian,
>>> u r trying to get q14 fixed point format but dsplib
>>> has q15 format, i suggest u to use both in same format . u can
>>> multiply with 2^15 . And two q15 multiplication results q2.30. here 2
>>> sign bit presents so u hav to modify that according to ur desired
>>> output format. i hope it will help u , if u hav any prob u can send me
>>> message.
>>>
>>> regards misan
>>>
>>> */Christian Narvaez /* wrote:
>>>
>>> Hi,
>>> I am having a problem trying to implement an IIR filter on an TI c55x.
>>> I have calculated the filter on matlab getting the following
>>> coefficients for 2 second order sections:
>>>
>>> SOS
>>> 1.0000 1.6854 1.0000 1.0000 -1.7197 0.8565
>>> 1.0000 -1.9999 1.0000 1.0000 -1.8899 0.9250
>>> G
>>> 1.0000
>>> 0.1041
>>> 1.0000
>>>
>>> Simulations perform as expected.
>>> Since the coefficients are between ]-2..2[ I transform the SOS matrix
>>> as SOS_fix = SOS*2^14:
>>>
>>> SOS_fix
>>> 16384 27614 16384 16384 -28175 14033
>>> 16384 -32766 16384 16384 -30964 15155
>>>
>>> The question is: can I run this coefficients on iircas5 of the TI
>>> dsplib? I know dsplib is Q.15 while my coefficients are Q.14, but I
>>> suppose this is not a problem if the filter's input is small
>>> enough not
>>> to cause any overflow. Unfortunately this does not work, the
>>> output is
>>> completely wrong.
>>>
>>> The second think I tried was to multiply the numerator
>>> coefficients of
>>> the second section of the filter by 0.1041 (according to G), before
>>> converting them to Q.14, getting this:
>>>
>>> SOS_fix_G
>>> 16384 27614 16384 16384 -28175 14033
>>> 1706 -3412 1706 16384 -30964 15155
>>>
>>> But this also does not work.
>>>
>>> Does anyone have any idea how I should convert my coefficients in
>>> order
>>> to work with iircas5?
>>>
>>> Thanks.
>>>
>>> Christian
> Start a New Thread