Reply by Jaime Andres Aranguren Cardona●December 13, 20072007-12-13
> Well, if you find a way to do it let me know because I am trying to create
> a low noise third octave graphics equalizer. Hence my other question to
> the NG about the overhead in doing 64 bit v 32 bit float on SHARC. I could
> code it and measure it but was hoping somebody could give me a rough
> estimate so I could know whether it's worth the effort.
Dirk,
I think I should have replied on your other thread, but here it goes anyway:
Why do not you use the 40 bit floating point in SHARC? This would be NO
overhead at all, still you get 32 bits precision (mantissa) and 8 bit
exponent.
Regards,
--
Jaime Andres Aranguren C.
SanJaaC Electronics
Soluciones en DSP
www.sanjaac.com
--
Posted via a free Usenet account from http://www.teranews.com
Reply by Jerry Avins●December 11, 20072007-12-11
robert bristow-johnson wrote:
> On Dec 10, 9:13 pm, Jerry Avins <j...@ieee.org> wrote:
>> robert bristow-johnson wrote:
>>> ... (a.k.a. "bandaxall") ...
>> Should that be "Baxendall" or is that something else?
>>
>
> no, you're virtually correct, Jerry:
>
> http://www.schmarder.com/radios/tech/tone.htm
>
> but it's amazing how many google hits you get with "bandaxall" and get
> references to guitar amp tone controls.
>
> anyway, i misused the term. i first heard it in reference to the
> standard *shelving* filters, not peaking EQ, but i swapped it in my
> memory for lack of a fresh reference.
Well, I built my first James circuit around i952. The response has
"lumps": if you set the bass control to full boost, there's a slight dip
just above the frequency where the boost begins. With full cut, there's
a slight dip. The same action is reflected in the treble control. You'll
see it again if you convert the basic circuit to a feedback (i.e.
Baxendall) control. The effect isn't mitigated by separating the base
and treble sections by a buffer stage. Around 1960, I showed how to
eliminate the effect by using center-tapped pots and connecting the
sliders to the center taps.
Although it nearly mimics a two-break circuit -- start of slope/end of
slope -- it is actually a four-break circuit with one pole /nearly/
canceling one of the zeros. The further from flat the control is set,
the more the cancellation is upset. Tying slider to the center tap keeps
pole and zero aligned. I doubt that anyone alive can gear the dip, but I
can measure it, so my heart rejoices when I know it's gone. :-)
The pictures in the cited article is a common cheat; it doesn't show a
lump. You'll see it clearly with one control set to flat and the other
to full boost (or cut).
Jerry
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
Reply by Dirk Bruere at NeoPax●December 11, 20072007-12-11
Vladimir Vassilevsky wrote:
>
>
> Dirk Bruere at NeoPax wrote:
>
>
>>> It turns out that it is absolutely unnecessary to have 30 biquad
>>> sections; somewhat 7-8 sections will do quite well for pretty much
>>> any practical case.
>>
>>
>> Except where the "practical case" is a graphics equaliser in the home
>> or studio.
>
> Let's wait till you will grow wiser. I will keep you plonked you until
> then, OK?
>
> VLV
>
I know you - you're Phil Allison!
--
Dirk
http://www.transcendence.me.uk/ - Transcendence UK
Remote Viewing classes in London
Reply by Ron N.●December 11, 20072007-12-11
On Dec 11, 9:57 am, robert bristow-johnson <r...@audioimagination.com>
wrote:
> On Dec 11, 11:06 am, Vladimir Vassilevsky <antispam_bo...@hotmail.com>
> wrote:
>
> > Dirk Bruere at NeoPax wrote:
>
> > >> It turns out that it is absolutely unnecessary to have 30 biquad
> > >> sections; somewhat 7-8 sections will do quite well for pretty much any
> > >> practical case.
>
> > > Except where the "practical case" is a graphics equaliser in the home or
> > > studio.
>
> > Let's wait till you will grow wiser. I will keep you plonked you until
> > then, OK?
>
> seems to me to be pretty small potatoes (30 vs. 8 sections), quite
> unworthy of plonking.
>
> personally, i like the idea of 1/3 octave graphic rather than 1 octave
> spacing, just because i like to think of myself as a mathematical
> control freak (i.e. the more controllable parameters, the better).
Even if you want 30 or so sections, one isn't likely to
need to set the controls so that there are more than 8
or so moveable inflection points that create an audible
difference. As long as the number of inflection points
is reasonable, it might not matter how many control points
are being interpolated (1/12th octave or whatever) in the
frequency domain by a smaller number of parametric biquads.
(Of course, all bets are off if one is (mis)using a
graphics equalizer to create bizarre timbres so that,
say, a producer can create a "new" sound to help make
their cookie cutter pop star sound different from all
the others.)
IMHO. YMMV.
Reply by Vladimir Vassilevsky●December 11, 20072007-12-11
robert bristow-johnson wrote:
>>>> It turns out that it is absolutely unnecessary to have 30 biquad
>>>>sections; somewhat 7-8 sections will do quite well for pretty much any
>>>>practical case.
> personally, i like the idea of 1/3 octave graphic rather than 1 octave
> spacing,
No spacing. Graphic is just the way of representation of the frequency
response. You can have 65536 sliders; that doesn't make any difference
in the concept.
> just because i like to think of myself as a mathematical
> control freak (i.e. the more controllable parameters, the better).
Then you should like it: 8 biquads = 33 parameters.
> but practically you're probably right, Vladimir.
The goal is to approximate the desired response, and the function of the
16th order will do that pretty well for any reasonable EQ curve.
Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com
Reply by robert bristow-johnson●December 11, 20072007-12-11
On Dec 11, 11:06 am, Vladimir Vassilevsky <antispam_bo...@hotmail.com>
wrote:
> Dirk Bruere at NeoPax wrote:
>
> >> It turns out that it is absolutely unnecessary to have 30 biquad
> >> sections; somewhat 7-8 sections will do quite well for pretty much any
> >> practical case.
>
> > Except where the "practical case" is a graphics equaliser in the home or
> > studio.
>
> Let's wait till you will grow wiser. I will keep you plonked you until
> then, OK?
seems to me to be pretty small potatoes (30 vs. 8 sections), quite
unworthy of plonking.
personally, i like the idea of 1/3 octave graphic rather than 1 octave
spacing, just because i like to think of myself as a mathematical
control freak (i.e. the more controllable parameters, the better).
but practically you're probably right, Vladimir.
r b-j
Reply by Vladimir Vassilevsky●December 11, 20072007-12-11
Dirk Bruere at NeoPax wrote:
>> It turns out that it is absolutely unnecessary to have 30 biquad
>> sections; somewhat 7-8 sections will do quite well for pretty much any
>> practical case.
>
>
> Except where the "practical case" is a graphics equaliser in the home or
> studio.
Let's wait till you will grow wiser. I will keep you plonked you until
then, OK?
VLV
Reply by Dirk Bruere at NeoPax●December 11, 20072007-12-11
Vladimir Vassilevsky wrote:
>
>
> robert bristow-johnson wrote:
>
>
>> well, what it is that i'm trying to do without doing too much unpaid
>> work is first model the graphic EQ as a set of cascaded peaking EQs
>> with equal bandwidth (in log frequency) and that are equally spaced in
>> log frequency.
>
> [...]
>
> I prefer the different approach. The graphic EQ is just the way to
> represent the desired frequency response. The task is to approximate
> this response with whatever hardware you got. So it is down to design of
> the IIR filter to the arbitrary response. There are all sorts of
> shamanistic optimization methods to do that; works quite well indeed.
> It turns out that it is absolutely unnecessary to have 30 biquad
> sections; somewhat 7-8 sections will do quite well for pretty much any
> practical case.
Except where the "practical case" is a graphics equaliser in the home or
studio.
--
Dirk
http://www.transcendence.me.uk/ - Transcendence UK
Remote Viewing classes in London
Reply by Vladimir Vassilevsky●December 11, 20072007-12-11
robert bristow-johnson wrote:
> well, what it is that i'm trying to do without doing too much unpaid
> work is first model the graphic EQ as a set of cascaded peaking EQs
> with equal bandwidth (in log frequency) and that are equally spaced in
> log frequency.
[...]
I prefer the different approach. The graphic EQ is just the way to
represent the desired frequency response. The task is to approximate
this response with whatever hardware you got. So it is down to design of
the IIR filter to the arbitrary response. There are all sorts of
shamanistic optimization methods to do that; works quite well indeed.
It turns out that it is absolutely unnecessary to have 30 biquad
sections; somewhat 7-8 sections will do quite well for pretty much any
practical case.
Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com
Reply by robert bristow-johnson●December 11, 20072007-12-11
On Dec 10, 9:13 pm, Jerry Avins <j...@ieee.org> wrote:
> robert bristow-johnson wrote:
> > ... (a.k.a. "bandaxall") ...
>
> Should that be "Baxendall" or is that something else?
>
no, you're virtually correct, Jerry:
http://www.schmarder.com/radios/tech/tone.htm
but it's amazing how many google hits you get with "bandaxall" and get
references to guitar amp tone controls.
anyway, i misused the term. i first heard it in reference to the
standard *shelving* filters, not peaking EQ, but i swapped it in my
memory for lack of a fresh reference.
r b-j