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Megha-

Please post these questions to MATLAB group (m...@yahoogroups.com). 
They can help you figure out why your MATLAB code below is not yet
working.

-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 <j...@signalogic.com> 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...@yahoogroups.com 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

(You need to be a member of c54x -- send a blank email to c54x-subscribe@yahoogroups.com )

Thanks Jeff
I have forwarded this messag eon matlab group too.
Jeff I was testing my result at matlab with result at DSP and I am not getting same outputs. If
you get something from below calculations, Kindly reply.
Following are the 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);
 >> [sos,g] = tf2sos(b,a)
 
 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
 
 x =
 
        -1233
          424
         -933
         -933
        -1233
        -1984
         1009
         -225
         1766
         -140
         -333
         1416
          102
        -1217
          704
         1383
        -1966
 
 >> R = filter(b,a,x)
 
 R =
 
    -1.5358
   -13.1021
   -52.7019
  -135.9341
  -260.9256
  -414.7120
  -591.4483
  -783.6995
  -942.4701
  -962.3276
  -742.9542
  -291.2615
   241.9823
   647.3840
   786.9343
   655.2580
   360.7719
 
 Now calculations with normalized vector. I am using a factor of 3 as thats the highest number
which can be with 2 bits.
 >> sos = sos/3
 
 sos =
 
     0.3333    0.6695    0.3362    0.3333   -0.2695    0.0585
     0.3333    0.6667    0.3333    0.3333   -0.3029    0.1072
     0.3333    0.6638    0.3305    0.3333   -0.3859    0.2279
 
 >> sos = sos*32768
 
 sos =
 
   1.0e+004 *
 
     1.0923    2.1938    1.1016    1.0923   -0.8829    0.1918
     1.0923    2.1845    1.0923    1.0923   -0.9926    0.3512
     1.0923    2.1753    1.0830    1.0923   -1.2645    0.7467
 
  [b,a] = sos2tf(sosnew,g)
 
 R = filter(b,a,x)
  
  R =
  
     -1.5358
    -13.1021
    -52.7019
   -135.9341
   -260.9256
   -414.7120
   -591.4483
   -783.6995
   -942.4701
   -962.3276
   -742.9542
   -291.2615
    241.9823
    647.3840
    786.9343
    655.2580
    360.7719
 
 So its the same as before. 
 Now I need to check with the output I am getting at the DSP. In DSP I am using the iircas51
function and in taht they multiply the a1 coefficient of the biquad by a factor of 2. Now sos
is nothing but:

sos = [b01, b11, b21, 1 , a11, a21
           b02, b12, b22, 1, a12, a22
             :      :      :     :     :     :
           b0L, b1L, b2L, 1, a1L, a2L]

for biquads. In DSP I need to pass 5 coefficients for each biquads, and hence for each biquad I
am passing b0, b1, b2 , a1 and a2. Now as the DSP does calculation with a1 multiplied by 2, i
am simply multiplying the a1 in sos by 2 and using that for filter calculations. I have checked
this method and its working with other calculations (calculations where no quantization was
there). So now
 
 sos(1,5) = sos(1,5)*2
 sos(2,5) = sos(2,5)*2
 sos(3,5) = sos(3,5)*2
 
 sos =
 
   1.0e+004 *
 
     1.0923    2.1938    1.1016    1.0923   -1.7659    0.1918
     1.0923    2.1845    1.0923    1.0923   -1.9851    0.3512
     1.0923    2.1753    1.0830    1.0923   -2.5291    0.7467
 
g is same as before 0.0012. Didnt change its value.

 >> [b,a] = sos2tf(sos,g)
 
 b =
 
   1.0e+010 *
 
     0.1623    0.9739    2.4348    3.2464    2.4348    0.9739    0.1623

 a =
 
   1.0e+013 *
 
     0.1303   -0.7492    1.5729   -1.4518    0.5665   -0.0918    0.0050
 
 >> R = filter(b,a,x)
 
 R =
 
   1.0e+007 *
 
    -0.0000
    -0.0000
    -0.0000
    -0.0000
    -0.0001
    -0.0004
    -0.0012
    -0.0029
    -0.0070
    -0.0162
    -0.0362
    -0.0790
    -0.1693
    -0.3573
    -0.7445
    -1.5361
    -3.1435
 
 And if I run that on the DSP, I am getting following output:
 -46
 -347
 -1216
 -2740
 -4785
 -7423
 -10612
 -13227
 -13343
 -10014
 -4438
 1009
 4733
 6482
 6491
 5308
 
 Hence i am not getting the correct output. But if sos is in following form 
 sos =
  
    1.0e+004 *
  
      1.0923    2.1938    1.1016    3.2768   -1.7659    0.1918
      1.0923    2.1845    1.0923    3.2768   -1.9851    0.3512
      1.0923    2.1753    1.0830    3.2768   -2.5291    0.7467
 
 instead of prev one. that is if the 4th col is 1 as in original sos matrix and if g=1, I get
same values as I am getting from DSP. That is the output is same. 
 I hope I am clear. Hence I am wondering am I doing normalization wrong or am I passing wrong
values to the DSP? 
 Kindly tell me where am I going wrong.
 Kindly reply
 Thanks
 Megha

Jeff Brower <j...@signalogic.com> wrote: Megha-

Please post these questions to MATLAB group (m...@yahoogroups.com). 
They can help you figure out why your MATLAB code below is not yet
working.

-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...@yahoogroups.com 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

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