Limiters & VU meters

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carlmart
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Limiters & VU meters

Post by carlmart »

I decided to open this a different topic, separate from the other one on portable mic preamp, because in a way they are related.

One shows the peaking points and the other contains them.

Even if the easier to be done, and probably one of the most accurate ones, are the needle type meters, they are too large for a given size, and not to easy to see, except if you are at a few inches from it and with an static head.

As what I'm interested in are moving situations, involving film & video shooting situations, a single LED would be hard to see, so you need a bar following the audio levels, besides red/led peak leds close to the level pots.

The limiter question is a problem, which I don't know how to solve using a balanced chip like those from THAT or TI.

That is, I think a limiter should act on the first stage, and those I know as quite effective used transformers and an LDR (like Vactrol). Present ones, like those suggested by THAT or that used by Tascam, control the second stage and use a bunch of chips to accomplish the limiting.

For the VU meter I found a promising chip: BA6820

http://www.unitrel.pl/dane/uklady-scalone/ba6820.pdf

The only problem is it needs discrete separate LEDS, which are not easy to accommodate and assemble, space wise speaking.
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JR.
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Re: Limiters & VU meters

Post by JR. »

I'm probably repeating myself by now... I have done a lot of work with meters.

Looking at the rohm part I would be nervous about multiplex noise (4kHz?).

JR
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carlmart
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Re: Limiters & VU meters

Post by carlmart »

Which is the "rohm" part? the Vactrols?

What multiplex noise is that?

Where can I find more info about your work with meters?

AFAIK and from the ones I have found on my work, all meters used in film production are some kind of bar types, or work as if they were so.

That is there is LED group moving all the time, not single leds. You can them follow things just from the corner of your eye, which is very practical during location shooting.

They are also usually tri-color. so you can quite follow things quite well.
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JR.
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Re: Limiters & VU meters

Post by JR. »

carlmart wrote:Which is the "rohm" part? the Vactrols?
The rohm part in the link you provided... Perhaps read the data sheet at that link.
What multiplex noise is that?
The LEDs are mutliplexed with high side switch transistors.
Where can I find more info about your work with meters?
probably some in Wayne's threads about meters.

I have two different patents related to simultaneous peak/VU meters.
US04166245 Roberts
US05119426 Roberts
AFAIK and from the ones I have found on my work, all meters used in film production are some kind of bar types, or work as if they were so.
Bar graph displays use more current if LEDs are all in parallel. If you run bar graph LEDs in series you will waste less current but you need enough voltage in PS to stack up a bunch of LEDs.
That is there is LED group moving all the time, not single leds. You can them follow things just from the corner of your eye, which is very practical during location shooting.

They are also usually tri-color. so you can quite follow things quite well.
I have literally designed a few tens of meters over the decades, there is not a library of all those designs, and I probably forgot several by now.

Not rocket science but being efficient for battery operation is a little harder which is why I suggested maybe pulsing the leds on through a cap. Your eyesight will integrate the light as being on continuous.

JR
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carlmart
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Re: Limiters & VU meters

Post by carlmart »

I know the brand ROHM, but which is the norm that makes many parts as unsafe for health?

Is there anything you can do to cut the multiplex noise off?

I anyone selling any kits with your patented meters? Can they be small?

Wayne, are you reading this to tell which of your threads to go to?
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JR.
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Re: Limiters & VU meters

Post by JR. »

carlmart wrote:I know the brand ROHM, but which is the norm that makes many parts as unsafe for health?

Is there anything you can do to cut the multiplex noise off?
If you search meters on this forum you will find several discussions about managing meter noise. actually a lot more than that...
I anyone selling any kits with your patented meters? Can they be small?
I think there are a few meter kits around but I don't think any use my peak/VU approach..
sm_meter.jpg
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Here is a peak/VU meter I did for a friend's console company. I control the software (it's microprocessor based). I thought about selling a universal meter kit or psuedo kit. Basically a programmed micro that you connect to one or more, LED latch drivers that you can configure different ways with personality pins to make a very flexible number of configurations.

I never did this because there was not much interest and I am not really looking for another business project. .

JR
Wayne, are you reading this to tell which of your threads to go to?
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carlmart
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Re: Limiters & VU meters

Post by carlmart »

Please allow me to get primitive and simpler. What about this meter:

http://www.hobbykit.eu/hobbye/h1010.html

As an option, probably more expensive, the one based on the BA6820, which I think is an upgrade on the LM chips (or is it not)

Both use 12 LEDs, discrete unfortunately, but they would attend the response I'd like to have.

What would be the objections? Has anyone built anything like it?

Even if I did a search, I couldn't find other projects, but I didn't look at all the pages.
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JR.
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Re: Limiters & VU meters

Post by JR. »

Is there a question there?

The second (discrete) meter is driving all the leds in parallel so high current.

The scaling looks linear, every 0.5V or so... 6V FS or so...

I'd still try to put several LEDs in series to save current.

JR
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carlmart
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Re: Limiters & VU meters

Post by carlmart »

Well, the question was there: did anyone built anything similar to that?

High current is never a good thing on portable battery powered project.

Putting the LEDs in series would save current but lose dB markings to do so, right?

The IC project has the capacity for peak/hold, but I can't find current specs anywhere.
ricardo
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Re: Limiters & VU meters

Post by ricardo »

The Mk4 Soundfield used a PPM-like circuit driving LM3915 with 10x3dB steps. It has dot & bar modes but you can use dot mode and by connecting the LEDs in series, have a bar display. This saves loadsa current but you might need a bit more voltage.

I designed the PPM-like circuit to meet all the BBC & EBU PPM type tests but I cheated. The rectifier was peak-to-peak instead of peak. But no one ever complained.
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