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Very Easy, I'm Sure - Ideas on an audio flip flop

 
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Very Easy, I'm Sure - Ideas on an audio flip flop
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zachery
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Joined: 06 Jan 2004
Posts: 1

Post Very Easy, I'm Sure - Ideas on an audio flip flop Reply with quote
Hi all! First time post, so please be gentle!

I want to build a simple little circuit which has two inputs and one output, I want input #1 to all of be the output *unless* input #2 has ANY signal, in which case I want input #2 to be all of the output.

When input #2 is turned off (nil) again, I want input #1 to be all of output again...

Sounds easy...

This is for low power <stereo> audio signals, so I need minimum distortion - I built a quick model (based on a normal flip-flop DC circuit) and sound was oh so terrible!

All help/ideas appreciated!

Cheers,

Zac

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There are 10 types of people in the world: Those who can count in binary and those who can't.
Tue Jan 06, 2004 8:49 pm View user's profile Send private message
biascomms
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Joined: 23 May 2004
Posts: 2

Post Reply with quote
An "audio flip-flop" isn't quite what you need. The easiest way to switch audio is to use a CMOS switch - the 4066 for example. You will also need to detect the presence of audio on your auxiliary input - this is easily achieved with a diode-pump circuit driving a transistor. The transistor can be used to operate the CMOS gates and automagically select the audio input for you.

If you want the audio to mix - if, for example, you want to be able to mix music and a voiceover, you need a slightly different approach. Again, you use a diode-pump level sensor to operate a transistor, but the main audio path goes through a voltage-controlled amplifier (VCA). When the microphone signal is detected, the VCA gain is reduced, fading the music so that the speech is louder thean the music being talked over.

There are lots of circuit diagrams for both approaches on the 'net - try a Google search for "auto voiceover schematic" or "automatic audio source seletion schematic" or similar wording.

BIAS COMMS
Sun May 23, 2004 1:04 am View user's profile Send private message
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