>
> Harold Hallikainen wrote:
>
>> I'm wondering if a multi-channel (perhaps 8 channels) audio level
>> metering
>> chip (VU meter) with an SPI interface exists. It would be great if the
>> inputs were differential so they could be hung across a balanced audio
>> line. A PIC will then pull this data and update a graphic display. Right
>> now we're looking at individual balanced rectifier and filter circuits
>> driving analog inputs on a PIC. LOTS of parts! It'd be great to just
>> have
>> one chip handle the whole thing. Another possibility would be run all
>> this
>> into a DSP and calculate the levels, but, if a chip is already out there
>> that does this, it'd be great!
>>
>> Searching the usual suspects doesn't seem to turn up anyting.
>>
>> Ideas?
>
> Ummm, aren't you building this chip yourself? DSPIC with SPI interface,
> and
> 8 channels of A/D. Sample audio at 44khz, then rectify and filter
> digitally.
> You can put the needed prefilter into the differential to single
> ended op amp circuit.
>
> Why would you use balanced rectifiers and filters?
> Just do a balanced to single end conversion at the start and cut your
> parts
> count in half.
>
> Latest 'ideas for design in EDN mag) has a circuit for using a single
> transistor
> to do full wave rectification (just bias it right and use right gain set
> resistors).
>
> Using software for the whole thing gives you the advantage of being able
> to change the filtering, if needed.
>
> R
>


Thanks for the comments! I'm hoping to find a chip that already does the
job, but can either do this in analog hardware or software. The balanced
rectifier is an ideal rectifier circuit with a differential input. Our
incoming audio is balanced, not single ended. I'd like a chip where I just
feed it 8 balanced audio signals and all the VU levels show up on an SPI.
I may end up doing it in DSP. I'd probably still need the differential
amplifiers for each input.

Thanks for the comments! Any more?

Harold

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