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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 <j...@signalogic.com> 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 ^^ Q
>
>      This 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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Dear Jeff
When I calculate coeff from MATLAB, for 6 order i get following:
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

These are the three biquads. In sos we know in every row first three are "b" coeff
(for zero) and last 2 are "a" coeff (for poles). 
Are you saying that I should divide all my coefficients by max coeff (2.0085) in this case and
provide first 3 as "b" and last 2 as "a"?
Another thing I didnt understand is u said at output apply 1/k. Shouldnt we apply k instead of
1/k? We are dividing our coeffs by k and hence to get the output should we now multiply by k? 
And from your statement : "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." I understand that u
are saying I should apply the factor to the output i am writing on the device. Ex :
PEPwrite15(bufferxmt, hcodec);
Then I should write it as ;
PEPwrite15(k*bufferxmt,hcodec);
But in the above I can only write 16 bit data and if it exceeds that it will overflow.
I hope I am making myself clear.
If I am understanding anything wrong, kindly correct me.
Kinldy Reply
Thanking You
Megha Daga

Jeff Brower <j...@signalogic.com> 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 <j...@signalogic.com> 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 ^^ Q 
This 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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