Re: Audio
- From: tuurbo46@xxxxxxxxxxx
- Date: 14 Jan 2006 05:21:15 -0800
Richard Dobson wrote:
> tuurbo46@xxxxxxxxxxx wrote:
>
> > Hi
> >
> > I recently bought a starter kit to learn the area of DSP. One of my
> > projects i would like to carry out is to design a simple graphic
> > equaliser - 3 bands.
> >
> > The problem that i dont understand is the best range for each of the 3
> > bands. The values i have selected have been enclosed below. Please
> > could somebody advise me if these ranges are ok, or should they be
> > shifted?
> >
> > Filter one - 0Hz to 500Hz
> > Filter two - 500Hz to 2KHz
> > Filter three - 2KHz to 10 KHz
> >
> > Look foward to your advice.
> >
>
> In the most common arrangement, the "centre band" of an GEQ is set at 1000Hz,
> and further bands either side are at octaves or fractions/multiples of octaves
> above and below. So for a plain 3band bass/mid/treble system you might use 250,
> 1000, 4000. That is indeed not so far from your suggestions above (just change
> the 10Khz to 8Khz), but from the users point of view the bands are traditionally
> defined by Centre Freq, and the bandwidth is determined by the filter slope,
> e.g. up to 12dB/Oct (Pro EQs will allow some control of slope as well as the
> cut/boost amount), and the bandwidth boundaries are formally defined as the
> frequencies at which the response is down by 3dB. This is otherwise described as
> the "Q" of the filter (ratio of Cfreq to bandwidth). The filters will still
> pass significant audio beyond those limits - the responses overlap.
>
> All that said, the simple 3band EQ on my Behringer mixer has ranges centred on
> 80Hz, 2.5KHz, and 12KHz. Not, I have to say, very much use to me, except for
> primitive noise reduction, so I leave all pots centred on zero change, and trust
> that the overall response is flat! Of course, "professional" GEQs offer 1/3rd
> Octave steps, for very fine adjustments of tonal balance (e.g. to compensate for
> microphones with a known presence boost at 2KHz), or to help a sound cut through
> the mix; rather different tasks from primitive noise reduction. So where you
> place the bands depends partly on what the primary function of the EQ is.
>
> It is always a good idea to study existing examples (both software and hardware)
> to see and hear what they do; and then you have something to which to compare
> your own design.
>
> Note also that while the mid bands of an EQ are true bandpass/bandreject
> filters, it is often preferred thatthe lowest and highest are "shelving"
> filters, which is a slightly different design.
>
>
> Richard Dobson
Thanks for you advice. I will now have a play and see what i come up
with.
Thanks again
Tuurbo46
.
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