How would I sense the bass beat of a song

t.halton10

New Member
Hi, I'm a student and was wondering if you could help me find a suitable sound sensor that could be used to pick up the bass beat of a song. I am using a pic chip to program LEDs but I need a way of getting a bass beat of a song into current to act as a imput for the pic chip. My hope is that this will make a disco light that runs on the bass beat of a song. Any help will be much appreciated.
Tom
 

Tom2000

Senior Member
I'd probably do this in hardware. An op-amp low pass filter followed by a rectifier/filter with a time constant selected to pass the bass notes and drum. Maybe fed to an ADC input...

Tom
 

t.halton10

New Member
Thanks for your reply.

Is there any sensor I could plug directly into a digital (probably analogue) input on the PIC chip and use the programming to change the speed of the disco lights in proportion to the input?

- I dont have time to produce all the extra op-amp front end of a circuit like this, i am just wandering if a microphone would work as surely it produces a different voltage depending on the volume of the song / frequencey of the note that could be used to vary the program?

Thanks Again.

Tom
 

Coyoteboy

Senior Member
No easy way round this unless the bass beat is much louder than the rest of the frequencies, otherwise it would just react to "noise". You could, i suppose, mount a mic in a sealed box in which most of the higher frequencies would be removed and only the lower notes would get through....
 

Tom2000

Senior Member
No easy way round this unless the bass beat is much louder than the rest of the frequencies, otherwise it would just react to "noise". You could, i suppose, mount a mic in a sealed box in which most of the higher frequencies would be removed and only the lower notes would get through....
Great idea!
 

Coyoteboy

Senior Member
Cheers :) Came to me as I bent down below my worktop (speakers above), I noticed that the high notes were lost as they are fairly directional, and the bass sounded loud as ever.
 

moxhamj

New Member
If you have a line level signal (eg 1V peak to peak) you can do this with a low pass filter with one resistor (3c) and one capacitor (10c). If you need to get a microphone level up to line level that is still only an op amp (90c) and a few resistors. You do mention time is a problem. If you are time poor and cash rich there are lots of commercial devices to do this. But if you are a typical student you are more likely to be cash poor and time rich in which case fiddling about with a 324 op amp chip will be time well spent. If you want to pursue this avenue there are lots of people on this forum who can guide you through the process.
 

MFB

Senior Member
low-tech is best

I once used a very low-tech approach to control a mains dimmer from a base speaker. An off-the-shelf LC crossover filter module directed the audio to the base speaker and a low voltage light bulb was used to drive an LDR cell. The amplitude of the bass signal modulated the resistance of the LDR, which in turn flashed the mains lighting to the beat.

Even though you don’t need the mains isolation, you could try the same approach but using the LDR as one half of a potential divider, with its centre driving a PICAXE ADC input.
 
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