[Iain Churches]

I have brought this discussion with Joyhn Byrns
over from another thread, as it has the makings
of what might prove to be aninteresting project.



"John Byrns" wrote in message
...
In article ,
"Iain Churches" wrote:


John wrote

The LF and HF ranges of your proposed +/- 3 dB equalizer are obvious
enough, but it is not so obvious what you are talking about for the MF
range?

Before the days of parametric EQ, many recording consoles had three
band equalisers on most channels. The mid band was often termed
"presence" (particularly on broadcast consoles) and was centred at 3kHz
(the BBC used 2.6kHz IIRC)


The BBC analogue meter is no longer in production, though I do know
a source from which they can probably be obtained NOS.

I did not mean to imply and actual BBC meter should be used, I assumed a
peak reading meter circuit designed specifically for this project, or a
clone of the BBC circuit if desired. I assume that analog meter
movements are still manufactured, or am I wrong about this?

The BBC type is pretty funky. Two movements on one meter face,
green needle pointer for left, red needle pointer for right. White
lettering on a black background. Few people outside broadcast
have seen them. They are always a talking point.

See:
http://www.kolumbus.fi/iain.churches/Pics/BBC_PPM.jpg

What do you mean by the "Peter Baxandall topology"? When I think of a
"Peter Baxandall topology" I always think of his feedback tone control
circuit, but today many people, at least here on this usenet group, seem
to consider the "Baxandall" tone control circuit to be the standard
passive tone control circuit.

It is a long time since I read the Baxandall articles. IIRC the first
circuit was a feedback tone control as you describe. The passive
version arrived soon afterwards. The circuit was later modified for
use with guitar amps in the USA, and known by the name of James.

I would like to see some evidence of who
actually developed the common passive tone control circuit, it is not
obvious to me that it was "Peter Baxandall" was responsible for it as
many today claim, although it is possible, I don't know and would like
to see some evidence to settle the issue once and for all.

Peter Baxandall was the author of the articles which AFAIK first
described this tone control in a British journal. All the textbooks I
have seen attribute it to him also.

Unfortunately I don't think the passive topology, whoever may have
designed it, easily accommodates the addition of a "MF" band.

Agreed. I was thinking of Baxandall for a two frequency
control LF and HF ( I would probably never use the mid control)
but if one needs mid, then there are plenty of other options.


I have been giving this idea quite a bit of thought. There are a lot of
alternatives, but I have picked one as a starting point, although it is
difficult to proceed very far without having a better idea what you want
the "MF" equalizer to do? Could you provide some input on the
specifications desired for the "MF" equalizer? Once I have had a chance
to think a bit about the requirements for the "MF" equalizer, I will
write up my thoughts and post them here.

As mentiond before, I think it should be fairy wide Q and centred on
3kHz Personally, I could live without it.

Let me do some listening tests with a parametric set up as a three band
(I have some Neve modules) and I will see if I can find a compromise.
I am sure there is no "one size fits all" solution.

Best regards
Iain