Limiters & VU meters

Where we discuss new analog design ideas for Pro Audio and modern spins on vintage ones.
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carlmart
Posts: 169
Joined: Mon May 19, 2014 6:11 am

Re: Limiters & VU meters

Post by carlmart »

The first forum I posted was GroupDIY, but that was before I discovered this forum. I found this to be more tuned on what I wanted to achieve.
ricardo wrote:You've posted your questions in several fora. The easiest is the Sound Devices approach.
The SD approach, same as the Shure approach and others is to use transformers and LDRs. I can't afford using transformers.
Next is to have limited gain mike amp and a limiter as the second stage. I posted suggestions on how to make this work (the stuff about gain structure) This still applies.
This the path I will follow, and I'm trying to find out with THAT about using just the limiter parts and not the compander. The gain will be handled by a three position switch and a log pot just after the input 1501 and before the limiter stage.
This is usable with correct choice of OPA. But you need to do some work eg study datasheets of possible OPAs. Have you looked at my suggested OPA and tried to understand what makes it suitable?
I did look for several rail to rail OPAs that could handle a 12v single supply and I didn't find any that did. I looked into AD, TI and LT.
When you come up with your final working circuit, please post it here too. I think you owe it to those who have tried to help you.
Of course I will get back with the final solution.
Have you told THAT EXACTLY what you want?


Since the very beginning.
Have you studied the 23 x THAT Design Notes?


You mean those using compressors? Not all, just those that included limiters.

My EE partner is now getting into the game and will probably be around here this week too.
ricardo
Posts: 262
Joined: Sun Apr 10, 2011 7:24 am

Re: Limiters & VU meters

Post by ricardo »

carlmart wrote:The SD approach, same as the Shure approach and others is to use transformers and LDRs. I can't afford using transformers.
Don't forget the solution you linked to with 2x10k resistors. That will work. :)
I did look for several rail to rail OPAs that could handle a 12v single supply and I didn't find any that did. I looked into AD, TI and LT.
The one I suggested should work. Have you tried it or tried to understand why I suggested it? (BTW, I DID explain this)
Have you studied the 23 x THAT Design Notes?
You mean those using compressors? Not all, just those that included limiters.
I meant STUDIED them. The info is all there but you need to do some work too.

Hopefully, your friend will do the work.
carlmart
Posts: 169
Joined: Mon May 19, 2014 6:11 am

Re: Limiters & VU meters

Post by carlmart »

BTW, I already have the THAT limiter circuit that might work in my application.
Attachments
THAT limiter.jpg
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ricardo
Posts: 262
Joined: Sun Apr 10, 2011 7:24 am

Re: Limiters & VU meters

Post by ricardo »

carlmart wrote:BTW, I already have the THAT limiter circuit that might work in my application.
Looks good if a little complicated.

Which THAT Datasheet or Design Note is that from?
carlmart
Posts: 169
Joined: Mon May 19, 2014 6:11 am

Re: Limiters & VU meters

Post by carlmart »

THAT sent it to me, it was in no data sheet.

Apparently it does have some parts, a compander, that I will no need, so I need advice from them on how to do it.

I'm trying to get my EE partner in contact with them to solve this out.

The only THAT suggested limiters which I found "simpler", if we may call them so, were the ones for speakers and amplifiers. But the adjustment is different.

Except for the Leach limiter I mentioned, which has no parts values suggested, the others I found seem not too reliable for good audio quality on this application.
carlmart
Posts: 169
Joined: Mon May 19, 2014 6:11 am

Re: Limiters & VU meters

Post by carlmart »

Probably a tricky question, that I also asked THAT and they haven't answered yet.

I am not sure how pot levels relate to V+/2 points.

My idea had been to replace R14, non-inverting 3 in U2A, with a log pot, so I could control the channel level just before the limiter.

But I'm not sure if the level would be completely zeroed when it gets down to V+/2. Would it be?

If not I would have to control the channel level through Rg, which demands specialized pots (antilog), not that easy to find and probably more expensive. A path I didn't wish to follow.

Another option might a 10K log pot to ground just before C7.

After the limiter stage, there would be a dual log pot replacing R15 on both channels, that would work as master level before the 1646 I am using as output.
ricardo
Posts: 262
Joined: Sun Apr 10, 2011 7:24 am

Re: Limiters & VU meters

Post by ricardo »

carlmart wrote:The only THAT suggested limiters which I found "simpler", if we may call them so, were the ones for speakers and amplifiers. But the adjustment is different.
Which Datasheets or Design Notes are those from?
carlmart
Posts: 169
Joined: Mon May 19, 2014 6:11 am

Re: Limiters & VU meters

Post by carlmart »

ricardo wrote:
carlmart wrote:The only THAT suggested limiters which I found "simpler", if we may call them so, were the ones for speakers and amplifiers. But the adjustment is different.
Which Datasheets or Design Notes are those from?
http://www.thatcorp.com/datashts/dn03.pdf

http://www.thatcorp.com/datashts/dn04.pdf
carlmart
Posts: 169
Joined: Mon May 19, 2014 6:11 am

Re: Limiters & VU meters

Post by carlmart »

The comments I got from THAT point to two things on the limiter:

1) The HF boost (pre-emphasis) in front of the VCA (C6 & R11). It provides a treble boost above 1.6kHz, which I do not need. So I will not use it.

2) How to best measure things in order to activate the limiter when there's a peak. The suggested circuit, which I thought did attend my needs, has two compression loops -- one using the RMS detector from the 4315 and another with a peak detector. Which should I use? Which is the best way to do it?
carlmart
Posts: 169
Joined: Mon May 19, 2014 6:11 am

Re: Limiters & VU meters

Post by carlmart »

BTW, I tried to find more accurate information on the web, googling for audio limiters.

Except for a 20:1 compression ratio as present in all limiters, all else depends on the application. This article seemed to most informative, but it didn't throw too much light on my doubts.

http://www.doctorproaudio.com/doctor/te ... s_en.shtml
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