Audio Filter/A to D conversion

[matty6ribs]

Hi there,

I'm working on a project to take a line out signal from an audio source, and convert it into a dmx signal that has 10 steps from 0-5 v, in 0.5v increments.

I need to filter the input to get a rough apprixmation for bass, midrange and treble. There will 3 dmx signals, each controlling a lighting display.

The circuit layout is as follows..,

Input signal (line out) -> Filter -> Analogue - Digital Conversion -> ? -> DMX input

I'd like to know your advice on what way to filter the audio line out signal, since each filter will be processing the same signal. Could I use something like an audio crossover for example? Simpler the better.

Analogue - digital conversion could be tricky since there needs to be only 10 steps into the DMX input. Would be ideal if it were in 0.5V steps

? (may be needed, dependant on the A-D section) converts the output from the A-D into the 10 steps 0-5V, in 0.5v steps.

Any advice on what approach to take is very welcome.

Thanks!

 

[Nigel Goodwin]

I presume what you're trying to make is a 'sound to light' project, but using DMX lighting instead of simple bulbs?. As such you need pretty all of a sound to light unit except the output triacs, I would suggest you need these stages:

AGC input stage.
Three filters, low pass, band pass, high pass.
Optional - three seperate agc stages after the filters.
Three rectifier stages.
Micro-controller (PIC) reading the outputs of the three rectifiers and generating the DMX signals.

 

[matty6ribs]

Hi Nigel,

Sorry I forgot to mention I already have the DMX input taken care of, it will accept voltages of 0-5V. This is why I am trying to get steps of 0.5V, I only need 10 different levels.

You are correct, sound to light is the application. I presume the AGC is needed to boost the input signal for the filters?

Thanks for your help!

 

[Nigel Goodwin]

Hi Nigel,

Sorry I forgot to mention I already have the DMX input taken care of, it will accept voltages of 0-5V. This is why I am trying to get steps of 0.5V, I only need 10 different levels.

I that case simply scale the output of the rectifiers to 0-5V and apply it directly - presumably the DMX input uses an A2D?.

You are correct, sound to light is the application. I presume the AGC is needed to boost the input signal for the filters?

It's to keep a consistant signal level, otherwise you're continually altering the manual gain control to keep it working well.

 

[audioguru]

Your steps are linear but your hearing's response to loudness is logarithmic. So the top 3 or 4 steps will be at about the same loudness, a few steps in the middle will be spread out a little in loudness and the few steps at the bottom will be very far apart in loudness.

If you make the steps spaced logarithmically then they will be spaced equally from low loudness to fairly high loudness.
5.0V, 3.5V, 2.5V, 1.77V, 1.25V, 0.88V, 0.62V, 0.44V, 0.31V and 0.22V.