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### Topic: Graphic equalizer IC "MSGEQ7" (Read 3468 times)previous topic - next topic

#### Joegi

##### Apr 17, 2012, 09:26 amLast Edit: Apr 17, 2012, 10:24 am by Joegi Reason: 1
Hi,
I have some questions regarding the graphic equalizer IC "MSGEQ7". I want to lead the output signal of an lm386 (connected to an electret-mic) to a MSGEQ7 and 'fetch' the band-peak-values via an ARDUINO and recalculate the 7 bands into two bands. I want to display the result via two LED lines driven by two TLC59116 (:=two band peak-meter).

My first question is:
In the datasheet (s. picture) of the MSGEQ7 pin 8 is connected via a 200k resistor with VDD (+5V). As I don't have a 200k resistor I would like to use 3 x 68k (=204k + tolerances). I guess that this is o.k. for a qualitative peak-meter!?

Second question:
There is a 22k resistor shown at pin 5 (audio in). I saw wiring schemes without this resistor. Do I need it?

Third question:
I assume that the IC with VDD=+5V needs an audio-signal with a center voltage of 2,5V (as generated from the lm386), right?

Fourth question:
I assume that the seven bands (63Hz, 160Hz, 400Hz, 1kHz,
2,5kHz, 6,25kHz und 16kHz) mean "0Hz-63Hz", "0Hz-160Hz", ... and not "0Hz-63Hz", "63Hz-160Hz", ..., right?

#### Grumpy_Mike

#1
##### Apr 17, 2012, 10:03 amLast Edit: Apr 17, 2012, 10:04 am by Grumpy_Mike Reason: 1
Quote
I assume that the seven bands (63Hz, 160Hz, 400Hz, 1kHz,
2,5kHz, 6,25kHz und 16kHz) mean "0Hz-63Hz", "0Hz-160Hz", ... and not "0Hz-63Hz", "63Hz-160Hz", ..., right?

No wrong on both counts it is a band centered on the frequency mentioned. It is only a low order filter so these bands might overlap for loud inputs.

Quote
I would like to use 3 x 68k (=204k + tolerances). I guess that this is o.k. for a qualitative peak-meter!?

That will be fine.

The resistor on the audio in is to stop the left and right channel shorting out. If you have a mono input you have no need for it.

#### Joegi

#2
##### Apr 17, 2012, 10:46 am
...but to build a two band peak-meter with one band going from (roughly) "0 to 1kHz" and the other going from "1kHz to 16kHz" I could use this formulas:
Band1: (peak_63Hz + peak_160Hz + peak_400Hz + peak_1kHz) / 4
Band2: (peak_2,5kHz + peak_6,25kHz + peak_16kHz) / 3

- right?

#### Joegi

#3
##### Apr 17, 2012, 11:39 am
...o.k., the separation-frequency with the above formulas wouldn't be 1kHz, as the named frequencies are the center frequencies of the bands, but something between 1Khz and 2.5kHz!

#### Grumpy_Mike

#4
##### Apr 17, 2012, 12:13 pm

...but to build a two band peak-meter with one band going from (roughly) "0 to 1kHz" and the other going from "1kHz to 16kHz" I could use this formulas:
Band1: (peak_63Hz + peak_160Hz + peak_400Hz + peak_1kHz) / 4
Band2: (peak_2,5kHz + peak_6,25kHz + peak_16kHz) / 3

- right?

If that is what you want to do you are using the wrong chip, while this would give you something it would not have a very smooth frequency response, in other words there would be lots of pass band ripple. You would be better off just using a high order high pass and low pass filter.

#### Joegi

#5
##### Apr 17, 2012, 12:54 pm
Is there any IC that has a high order high- AND low pass filter with adjustable cut-off frequency?
Alternatively I could use a FFT, but on an Atmega this is too slow!(?)
But nevertheless, as the look, not the quantity, is most important, I will try the MSGEQ7 (maybe I will display more than two bands to get better results)!

#### Joegi

#6
##### Apr 17, 2012, 01:23 pm
What about the widths of the bands of the MSGEQ7. Are they all the same. That would result in little or no pass-band between 63Hz and 160Hz and much pass-band between 6.25kHz and 16kHz!?

#### Joegi

#7
##### Apr 17, 2012, 02:53 pm
Would the "max263" IC be a feasible solution for two band filtering? One could switch the cut-off frequency fast to get a two band filter out of a one band filter!?

#### Joegi

#8
##### Apr 17, 2012, 03:29 pm
...I read the first sentences of the max263's datasheet (at the moment I don't have time to read more) and there is written that the IC has two filter sections! Does that mean that I could use a low-Pass and a high-pass filter at the same time?

#### Grumpy_Mike

#9
##### Apr 17, 2012, 07:19 pm
Quote
Would the "max263" IC be a feasible solution for two band filtering? One could switch the cut-off frequency fast to get a two band filter out of a one band filter!?

It might be I have not used tat chip before. However the switch capacitor filtering chips I have used in the past have been a disappointment, with the switching noise getting into the pass band.
Yes it looks like you an have two filters at he same time.

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