Graphic Equalizer Display Filter - MSGEQ7

GopherT

Joined Nov 23, 2012
8,012
Hi, I have been following your posts an I am a little confused about your goal. On one hand you mention a color organ, then you discuss that the output sounds like modem noise.

This chip is only intended to separate the amplitude of each bin of frequencies with a peak detector, then send those values to the output pin in sequence (as the strobe is clicked). Finally, the peak that was detected is decreased by 10% each time the value is read until the value reaches zero or a newly read value is higher that the current value left on the peak detector capacitor.

This setup is best (originally intended) to be used with a multiplexer and seven lm3915 logrithmic display chips that convert the output voltage to display the value.

This filter chip is only intended to be part of a graphic display of the seven frequency ranges, not as a pass-through for channel separation. It is not intended to be listened to - it will have a lot of switching noise and terribly distorted since it is a peak-detected value that is decayed in steps with each read instead of in a linear (or log) fashion.

Finally, your concern about detecting the beat was answered above when you noticed the bleed from other channels. Also, drums and bass will have higher order harmonics so it will definately show a pulse across all your channels (bins)
 

Thread Starter

gerases

Joined Oct 29, 2012
177
Hi, I have been following your posts an I am a little confused about your goal. On one hand you mention a color organ
I do have a goal of building a color organ but I don't want to just build something and be done with it. I'm interested in electronics and as I learn something new, I sometimes have a not very related question. Is it because I'm posting in the Projects forum and not the General Chat forum?

This chip is only intended to separate the amplitude of each bin of frequencies with a peak detector, then send those values to the output pin in sequence (as the strobe is clicked). Finally, the peak that was detected is decreased by 10% each time the value is read until the value reaches zero or a newly read value is higher that the current value left on the peak detector capacitor.

This setup is best (originally intended) to be used with a multiplexer and seven lm3915 logrithmic display chips that convert the output voltage to display the value.

This filter chip is only intended to be part of a graphic display of the seven frequency ranges, not as a pass-through for channel separation. It is not intended to be listened to - it will have a lot of switching noise and terribly distorted since it is a peak-detected value that is decayed in steps with each read instead of in a linear (or log) fashion.
Excellent description of the chip, should be added to the datasheet.

then you discuss that the output sounds like modem noise.
I never intended to listed to the chip. But as I was listening to the music through a second jack that I jumped from the first jack (where the audio input was connected), I noticed the noise. So I asked.

Finally, your concern about detecting the beat was answered above when you noticed the bleed from other channels. Also, drums and bass will have higher order harmonics so it will definitely show a pulse across all your channels (bins)
As I'm waiting for different project parts in the mail, I'm stumbling upon what other people are doing, etc. So, I thought it was OK to ask those question in this thread.

crutschow has been awesome! I catch a general drift of arrogance from other members of the forum. Not you, but others. It's tempting to be arrogant when you know something highly technical and therefore little understood by the majority. If one resists that temptation, it's a big victory over oneself. But we're all prone to this unfortunately, probably even me to some extent -- but I'm much more aware of my own tendencies of this sort now that I've been on the forum and studies electronics for this little while.
 

Thread Starter

gerases

Joined Oct 29, 2012
177
You are making sense. It's just that the circuit is not a normal HP filter, instead it is a rather odd LP filter. It has a fixed gain at each of the frequency extremes with the LF gain higher than the HF gain. At DC or low frequencies the circuit is an inverter (phase = 180°) with a gain of 220k / 6.8k = 32.35. At high frequencies, well above the pole frequency, the amp becomes non-inverting (phase = 0°) with a gain of 1.

This circuit is commonly used as an all-pass filter (phase changes with frequency but gain is constant) if you set R10 equal to R11. For that configuration the low frequency gain is -1 (phase = 180°) and the high frequency gain is +1 (phase = 0).
Cool! Thanks for the analysis. I'm glad I wasn't totally off-base. Strange he used that circuit a frequency detector. It does say however, the whole circuit is for advanced experimenters.

Thanks!!!
 

Thread Starter

gerases

Joined Oct 29, 2012
177
This setup is best (originally intended) to be used with a multiplexer and seven lm3915 logrithmic display chips that convert the output voltage to display the value.
This is very interesting. I'll look into this as well!
 

Thread Starter

gerases

Joined Oct 29, 2012
177
Just to be clear, each LM3915 will drive a 10 segment bar graph segment. Your MSGEQ7 display chip will slice the audio signal into 7 bins (channels) of frequency ranges and the intensity of each.
I see. So they can't be used together?
 

Thread Starter

gerases

Joined Oct 29, 2012
177
The AGC circuit is awesome but I can't quite understand a few things about it. First, how come no base resistor on Q1? With a 20v max signal, don't we need it? Also what exactly determines the 0-1.2 drop on the pot? If we wanted it to be 3 what would need to be changed? Assuming of course the input is over 3?
 

GopherT

Joined Nov 23, 2012
8,012
I see. So they can't be used together?
Sorry for the misunderstanding, they can be used together. I was just trying to clarify that you will need one lm3915 for each channel on your chip (7 band equalizer requires 7 lm3915 chips).
 
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Thread Starter

gerases

Joined Oct 29, 2012
177
Sorry for the misunderstanding, they can be used together. I was just trying to clarify that you will need one lm3915 for each channel on your chip (7 band equalizer requires 7 lm3915 chips).
Aah, I get it now. The other day I accidentally gave 10v through my function generator. It seems to be still working fine. Is it possible I damaged it?
 
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