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MSGEQ7-Based DIY Audio Spectrum Analyzer for BADASS Display

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rheslip0
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Re: Re MSGEQ7: Nice chip
rheslip0   7/9/2014 2:02:54 PM
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Another approach - use the Teensy 3.1 and audio shield from pjrc.com. You only need one processor which is Arduino compatible so you can use the Neopixel libraries. They have a really nice audio DSP library including up to 1024 bin FFTs for the ARM M4 core. Teensy board about $20, audio sheild about $15. It will blow the doors off your solution:

https://www.youtube.com/watch?v=CblOUmK3oKM

I'm not associated with PJRC but I am very impressed with their products. I beleive they also have a high performance LED strip driver too.

Rich H

 

Max The Magnificent
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Re: Re MSGEQ7: Nice chip
Max The Magnificent   7/9/2014 1:13:50 PM
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@jambrose: We (Mixed Signal Integration) also have a 1/6th octave Low Power Spectrum Analyzer IC; the MSLSA.  The outputs are 6 AC outputs and you can easily cascade the devices.

Very interesting -- I'm printing off the datasheet as we speak...

jambrose950
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Re MSGEQ7: Nice chip
jambrose950   7/9/2014 1:00:41 PM
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We (Mixed Signal Integration) also have a 1/6th octave Low Power Spectrum Analyzer IC; the MSLSA.  The outputs are 6 AC outputs and you can easily cascade the devices.  Here is a link:

http://www.mix-sig.com/index.php?option=com_content&view=article&id=128:mslsa&catid=52


Samples and evaluation boards are available.  

jambrose950
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Re: MSGEQ7 Nice chip
jambrose950   7/9/2014 12:51:31 PM
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Yes, you can adjust the 33 pF and 200 kohm RC values to achieve different clock frequencies. However the filters are quite wide, so the effect would be minimal.   Others have found the interpolation technique  in firmware gives better results. 

Max The Magnificent
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Re: Nice chip
Max The Magnificent   7/8/2014 6:23:27 PM
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@David: However that leads me to my question...with only 7 frequency bands and 2 channels will your BADASS display now only have 14 channels instead of the 16 in the diagram?

Thsi is something I've been pondering -- I think interpolating between two channels to create an additional channel would give me a quick fix. Of course, when I move onto doing all thus in software using an FFT (or similar algorithm), I'll be able to split things up into as many "buckets" as I wish.

 

Max The Magnificent
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Re: Nice chip
Max The Magnificent   7/8/2014 6:20:52 PM
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@Rcurl: I notice that you can set the oscillator frequency of the chip externally. I wonder if you could intentionally skew the oscillator frequency of a second chip being fed the same audio input to get some extra bands in between the intended ones?

Oooh -- that is an interesting idea...

 

Max The Magnificent
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Re: Nice chip
Max The Magnificent   7/8/2014 6:19:55 PM
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@David: I would have preferred a  few more frequency bands but  really for a display that would probably be overkill

I agree -- the more the merrier -- even just one more would have been ideal for my purposes, but we're engineers -- we have to make do with what's available LOL

David Ashton
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Re: Nice chip
David Ashton   7/8/2014 6:10:38 PM
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@Rcurl....nice idea.  I saw a similar thing done recently with the good old LM3915 LED level meter chips to give 1dB increments instead of the usual 3dB.    And I got some chips that generate and provide a notch filter for 2600Hz tones used in Radio keying systems, I was going to underclock them to get the notch down to 1000Hz.  However in this case, according to Max's diagrams, the bands are fairly wide anyway, so I don't know if you'd really gain much here?

Rcurl
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Re: Nice chip
Rcurl   7/8/2014 5:48:59 PM
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@David: "However that leads me to my question...with only 7 frequency bands and 2 channels will your BADASS display now only have 14 channels instead of the 16 in the diagram?"

I notice that you can set the oscillator frequency of the chip externally. I wonder if you could intentionally skew the oscillator frequency of a second chip being fed the same audio input to get some extra bands in between the intended ones? 

David Ashton
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Nice chip
David Ashton   7/8/2014 5:01:43 PM
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That is certainly a neat little chip Max.  I would have preferred a  few more frequency bands but  really for a display that would probably be overkill.

However that leads me to my question...with only 7 frequency bands and 2 channels will your BADASS display now only have 14 channels instead of the 16 in the diagram?

I guess having sampled all 7 bands you could interpolate between adjacent values to get more "Pseudo" channels....?

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