Compression VU meter schematic

[vumetros]

Hi guys

First post here

I am building a custom stereo compressor and I would like to put a VU meter to show the amount of compression (db)

I am guessing I would need some kind of a comparator comparing the compressed signal to the uncompressed

Are there any circuits / schematics that would help me get some inspiration?

Thank you in advance

 

[Rob Flinn]

Normally they are just derived from the sidechain control signal & scaled toproduce the right reading on the meter.

 

[thomasdf]

I've been thinking for a while of a (digital?) meter driver comparing the input and output and displaying a input/output relation, like on some plugins (think Klanghelm MJUC).
I think that's a cool feature sometimes but it seems almost impossible to do in the analog domain ? The differences between program and silence would make the in/out very hard to measure and display.
For instance, I like that on the Eventide Omnipressor it displays the output gain added to the gain reduction. If the needle stays around 0 you know the makeup covers for the gain reduction. Super smart !

 

[volker]

Hi guys

First post here

I am building a custom stereo compressor and I would like to put a VU meter to show the amount of compression (db)

I am guessing I would need some kind of a comparator comparing the compressed signal to the uncompressed

Are there any circuits / schematics that would help me get some inspiration?

Thank you in advance

There are different ways to achieve this for different types (opto, JFET, VCA, vari-µ) of compressors. What circuit are you building?

 

[JohnRoberts]

Hi guys

First post here

I am building a custom stereo compressor and I would like to put a VU meter to show the amount of compression (db)

I have killed a lot of brain cells designing meters over the decades and even a few compressors along the way.

A meter showing amount of compression is not typically used, closest would be a meter showing how much gain reduction is occurring that could indicate rough compression when combined with an input/output level meter.

I am guessing I would need some kind of a comparator comparing the compressed signal to the uncompressed

This is pretty much the amount of gain reduction... Not technically a "comparator" that generally compares DC voltage levels. So you need to process the signal to extract loudness not unlike a VU meter and convert levels to dB to get a delta dB amount. .

Are there any circuits / schematics that would help me get some inspiration?

What you are asking for has not been done AFAIK, so nothing obvious to copy. In the digital domain one could sample and crunch multiple signal levels and display whatever you want. If there was a compelling need for this I expect someone would have done this by now. Meters and compressors are both mature technology.

Consider a more conventional gain reduction meter.

Thank you in advance

Sorry for no solutions but sometimes thats how it goes. Keep thinking.

JR

 

[vumetros]

Hi guys

Thank you for the replies!

The compressor I am working on is an opto one.

I am guessing a gain reduction meter would do the job

 

[Brian Roth]

Look at the schematics for the UREI LA2, LA3, and LA4 compressors......all are opto.

LA 2 and LA3 are somewhat similar (LA2 uses vacuum tubes) and both use an electroluminescent light source to "shine" on the photoresistor gain control element. Both use a second photoresistor to control the gain reduction readings on a VU meter.

LA4 uses a LED light source and has a different method to control the VU meter for gain reduction readings.

Those units are "classics" in a bazillion recording studios.

Bri

 

[JohnRoberts]

Hi guys

Thank you for the replies!

The compressor I am working on is an opto one.

I am guessing a gain reduction meter would do the job

Optos don't have well behaved gain laws but there are workable approximations.

JR

 

[vumetros]

Thank you for the suggestions!

I will look into LA2,3,4 to copy/adjust one of their meter drivers

 

[scott2000]

The Forssell opto compressor has gr metering too.

 

[gyraf]

opto gain reduction is monitored by having a proxy opto with its light source in parallel/series (EL/LED) with the audio opto, then monitoring this as a voltage divider against a set reference. This why GR meters traditionally go "backwards" on a vu-meter