Re: DSP Trick: Fixed Point DC Blocking Filter with Noise-Shaping

On Mar 13, 12:37 pm, Rick Lyons <R.Lyons@_BOGUS_ieee.org> wrote:

> Hello EB,
>
>   In the March issue of the IEEE Sig. Processing
> Magazine, Randy Yates gives his description of a
> fixed-point DC blocker.  His material is in the
> "DSP Tips & Tricks" column of the magazine.

Thanks. I haven't gotten my copy yet and the online version isn't
available either. Looking forward to it though.

Eric (EB)

On Mar 13, 12:37 pm, Rick Lyons <R.Lyons@_BOGUS_ieee.org> wrote:

> Hello EB,
>
>   In the March issue of the IEEE Sig. Processing
> Magazine, Randy Yates gives his description of a
> fixed-point DC blocker.  His material is in the
> "DSP Tips & Tricks" column of the magazine.

Thanks. I haven't gotten my copy yet and the online version isn't
available either. Looking forward to it though.

Eric (EB)

On Mar 13, 12:37 pm, Rick Lyons <R.Lyons@_BOGUS_ieee.org> wrote:

> Hello EB,
>
>   In the March issue of the IEEE Sig. Processing
> Magazine, Randy Yates gives his description of a
> fixed-point DC blocker.  His material is in the
> "DSP Tips & Tricks" column of the magazine.

Thanks. I haven't gotten my copy yet and the online version isn't
available either. Looking forward to it though.

Eric (EB)

On Mar 13, 12:37 pm, Rick Lyons <R.Lyons@_BOGUS_ieee.org> wrote:

> Hello EB,
>
>   In the March issue of the IEEE Sig. Processing
> Magazine, Randy Yates gives his description of a
> fixed-point DC blocker.  His material is in the
> "DSP Tips & Tricks" column of the magazine.

Thanks. I haven't gotten my copy yet and the online version isn't
available either. Looking forward to it though.

Eric (EB)

On Mar 13, 12:37 pm, Rick Lyons <R.Lyons@_BOGUS_ieee.org> wrote:

> Hello EB,
>
>   In the March issue of the IEEE Sig. Processing
> Magazine, Randy Yates gives his description of a
> fixed-point DC blocker.  His material is in the
> "DSP Tips & Tricks" column of the magazine.

Thanks. I haven't gotten my copy yet and the online version isn't
available either. Looking forward to it though.

Eric (EB)

On Mar 13, 12:37 pm, Rick Lyons <R.Lyons@_BOGUS_ieee.org> wrote:

> Hello EB,
>
>   In the March issue of the IEEE Sig. Processing
> Magazine, Randy Yates gives his description of a
> fixed-point DC blocker.  His material is in the
> "DSP Tips & Tricks" column of the magazine.

Thanks. I haven't gotten my copy yet and the online version isn't
available either. Looking forward to it though.

Eric (EB)

On Mar 13, 12:37 pm, Rick Lyons <R.Lyons@_BOGUS_ieee.org> wrote:

> Hello EB,
>
>   In the March issue of the IEEE Sig. Processing
> Magazine, Randy Yates gives his description of a
> fixed-point DC blocker.  His material is in the
> "DSP Tips & Tricks" column of the magazine.

Thanks. I haven't gotten my copy yet and the online version isn't
available either. Looking forward to it though.

Eric (EB)

On Mar 13, 12:37 pm, Rick Lyons <R.Lyons@_BOGUS_ieee.org> wrote:

> Hello EB,
>
>   In the March issue of the IEEE Sig. Processing
> Magazine, Randy Yates gives his description of a
> fixed-point DC blocker.  His material is in the
> "DSP Tips & Tricks" column of the magazine.

Thanks. I haven't gotten my copy yet and the online version isn't
available either. Looking forward to it though.

Eric (EB)

On Mar 13, 3:05 pm, emeb <ebromba...@gmail.com> wrote:
>
> OK - I did some digging and my approach is similar to "Tim's Quicker
> DC Blocker" as described here:
>
> http://groups.google.com/group/comp.dsp/msg/3759bc4014951a03
>
> Tim's algo:
>
>     y[n]   = x[n] - Quantize{ w[n] }
>
>     w[n+1] = w[n] + (1-pole)*y[n]

scaling w[n] so that it works in an integer machine:

     y[n]   = x[n] - (w[n]>>scale);  // quantization happens here
     w[n+1] = w[n] + A*y[n];

where      A = (2^scale)*(1-pole)

> Mine:
>
>     d[n]   = x[n] - ( w[n] >>> scale ) ; note - full precision, so
> extend lsbs of d[n]

in other words, you have bits to the right of the binary point in
d[n], right?  i'd like to reword the alg (by scaling the quantitative
meaning of d[n]) so that it is represented as something you can
program in an integer machine (say, in C code) ...

>     w[n+1] = w[n] + d[n]
>
>     y[n]   = Quantize{ d[n] } ; just drop extra lsbs added in step 1

... so here is my spin of EB's alg:

    d[n]   = (x[n]<<scale) - w[n];
    y[n]   = d[n]>>scale;    // quantization happens here
    w[n+1] = w[n] + y[n];

the net operation happening to that state, w[n], is:

     w[n+1] = w[n] + x[n] - w[n]*2^(-scale)
            = (1 - 2^(-scale))*w[n] + x[n]
            = p*w[n] + x[n]
or
     z*W = p*W + X

    W/X = 1/(z-p)

where p = pole = 1 - 2^(-scale).

and output, y[n]:

     y[n] = x[n] - w[n]*2^(-scale)
          = x[n] - w[n]*(1-p)
or
    Y = X - W*(1-p)  =  X - (1-p)/(z-p)*X
      =  X*( 1 - (1-p)/(z-p) ) = X * (z-1)/(z-p)

so the transfer function is the high-pass filter

   H(z) = (z-1)/(z-p)

as it should be.  so if your pole is restricted to the values 1 - 2^(-
scale), this works.  but is it the same thing as Tim's?  i don't think
it's as concise.  maybe it's equivalent to my approach, but it looks a
little different.

the other thing that i wonder is if Eric's method effectively does the
noise shaping or fraction saving on the dropped bits.  that will take
a little more effort for me to figure out and i'll get to it
later.

> With no quantization or leaky integrator this seems to work fine. DC
> estimate doesn't decay as it does with leaky integrator, but that
> hasn't been a problem.

if there is no leakiness to the integrator (i.e. scale=0), the
integrator completely undoes the differentiator and no DC gets
blocked.

r b-j

emeb <ebrombaugh@gmail.com> writes:

> On Mar 13, 12:37 pm, Rick Lyons <R.Lyons@_BOGUS_ieee.org> wrote:
>
>> Hello EB,
>>
>>   In the March issue of the IEEE Sig. Processing
>> Magazine, Randy Yates gives his description of a
>> fixed-point DC blocker.  His material is in the
>> "DSP Tips & Tricks" column of the magazine.
>
> Thanks. I haven't gotten my copy yet and the online version isn't
> available either. Looking forward to it though.
>
> Eric (EB)

Hi Eric,

I just placed it on the web site:

  http://www.digitalsignallabs.com/dcblock.pdf

-- 
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%% Fuquay-Varina, NC            %  is say I'm sorry, 
%%% 919-577-9882                %  that's the way it goes..."
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