Read audio voltage level from LXR-3 in arduino

I have a balanced audio connection via and LXR-3 port and I need to read the voltage/decibel level of the audio. I have included the circuit of what I think I need to read it. I left the voltage divider values blank because I don’t know what they should be. The “arduino volt” divider needs to drop the voltage by half, and the “audio volt” divider needs to create about a 25% drop. any help on values would be great. If this is wrong any help would be great.

P.S. I know fritzing is not the best.

I assume you're trying to read dB SPL? That's been done, but there are many "complications". If you [u]search the forum[/u] you can find lots of discussion.

The "arduino volt" divider needs to drop the voltage by half, and the "audio volt" divider needs to create about a 25% drop.

Why? See [u]voltage divider[/u]. Two equal value resistors will cut the voltage in half. In most audio circuits the resistors can sum-up to about 10K.

The easiest way to "get started" is with a [u]microphone board[/u]. It's got a mic, preamp, and an "Arduino ready" biased output, and it's cheap. (That particular board doesn't have a gain control.)

I have a balanced audio connection via and LXR-3 port and I need to read the voltage/decibel level of the audio.

Is it line-level or a microphone?

Balanced connections usually need a differential amplifier. Microphones need a preamp and studio condenser microphones need 48V phantom power.

You can find examples of op-amp differential amplifiers on the Internet. If you have a line-level signal you can build one with a "gain" of 1 to convert the differential (balanced) signal to unbalanced.

Generally, you can ground one signal line and use the signal unbalanced but that's a bad idea if the signal is being used somewhere else and you want to keep it balanced. You also have to be careful and check the specs of whatever you're connecting because you're shorting one signal wire to ground.

In any case the Arduino can't read the negative half of the AC audio waveform (it can be damaged by negative voltages and you can damage/distort the audio signal). You can bias a regular line-level unbalanced audio signal with a voltage divider (2 equal-value resistors) to bias the input at 2.5V. That allows you to read the negative-half of the AC audio signal. Then, add a capacitor to "isolate" the bias from your audio circuit ([u]example[/u]). 10k resistors and a 1uF capacitor will work. (The audio comes-in through the capacitor and the resistor & capacitor junction goes to the Arduino input.)

With the input biased at 2.5V the ADC should read about 512 with silence, and you can subtract that out.

NoraTheDoggo: I have a balanced audio connection via and LXR-3 port and I need to read the voltage/decibel level of the audio. I have included the circuit of what I think I need to read it. I left the voltage divider values blank because I don't know what they should be. The "arduino volt" divider needs to drop the voltage by half, and the "audio volt" divider needs to create about a 25% drop. any help on values would be great. If this is wrong any help would be great.

P.S. I know fritzing is not the best.

Well I am experienced in reading circuit diagrams and your diagram is undecipherable to me - no idea what your circuitry does after staring at it.

Can you redraw using the normal conventions please, signal flow left to right, without confusing long wires everywhere, as a hand-drawn sketch? Name signals, lose the rats-nest layout by breaking into sections if needs be - maybe lose all the relays if they aren't relevant to understanding the signal acquisition parts. Draw opamps with the opamp symbol, not as a box.

BTW I'd expect an opamp in differential amplifier mode somewhere, or a differential ADC

Thanks for the help DVDdoug

Is it line-level or a microphone? I'm not sure what that means, but it is the output of a sound board so line-level?

Why? See [u]voltage divider[/u]. Two equal value resistors will cut the voltage in half. In most audio circuits the resistors can sum-up to about 10K. This doesn't talk about balanced audio voltage dividers with 3 resistors and all I need from that is the formula for that.

You can find examples of op-amp differential amplifiers on the Internet. If you have a line-level signal you can build one with a "gain" of 1 to convert the differential (balanced) signal to unbalanced. I have a voltage comparator the lm311p this would work right? I have followed the circuit to use for it, but I'm not sure if it will work with audio. It's rated for the voltage, and balanced connections are DC so it will work.

The only thing I need for this is the balanced audio connection voltage divider formula. Anyone who knows it, it would be a huge help.