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Megha-
> Are you saying that I should divide all my coefficients by max coeff (2.0085) in
> this case

Yes.
> and provide first 3 as "b" and last 2 as "a"?

That I don't know.  You have to study MATLAB docs and figure out which are numerator
and which are demoninator coefficients, and compare to TI docs.  A good problem for
new DSP students.
> 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?

Yes -- sorry if I was confusing.  To scale the coefficients, divide by k.  To restore
correct gain on D/A output, 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.

At first, don't multiply by k, just check with tone generator input to verify you get
the correct filter response.  Then, you can look inside PEPwrite15() to see if you
can output 20-bit or 24-bit values to the AIC23B.  Another alternative is to multiply
by k anyway, even though values are Q15, but keep the AIC input (filter input) very
low and hopefully avoid overflow.

-Jeff
> 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 ^^ 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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