help with volume limiting,,, Hard limiter,, no good

[nana7]

Hi there, I need help with a curcit design.
I can get plans for a "Hard limiter" for headphone amplifiers, but the result is a limited sound (good!) but it is done by clipping the sound.
Can it be done with out clipping, and just maintaining a minimum level, with out clipping the sound, and not going over a determnaed volume?
I guess so, isn’t that what the safe volume limiting system dose on a CD Discman and Minidisk ????

also can this come as a off the shelf chip?

Please help.
chers

 

[Optikon]

Hi there, I need help with a curcit design.
I can get plans for a "Hard limiter" for headphone amplifiers, but the result is a limited sound (good!) but it is done by clipping the sound.
Can it be done with out clipping, and just maintaining a minimum level, with out clipping the sound, and not going over a determnaed volume?
I guess so, isn’t that what the safe volume limiting system dose on a CD Discman and Minidisk ????

also can this come as a off the shelf chip?

Please help.
chers

might be able to do it with an AGC (automatic gain control) circuit somewhere in this path. You can allow maximum signal to top out without clipping.

 

[Nigel Goodwin]

What you're looking for is a compressor/limiter - which are basically the same device, but set up and operated in a different way. A compressor will compress EVERYTHING that goes through it, where a limiter passes everything through untouched, UNTIL the signal passes the preset level, when it starts to compress.

There used to be a range of custom IC's for this sort of thing, but I suspect they are long obselete?.

 

[audioguru]

My 1975 car radio used a forward-biased diode on each channel to limit the signal to the cassette recorder. It attenuated the signals way down before the diodes so that the distortion wasn't audible. Of course it rectified and filtered its output to control the forward bias on the diode.
It worked about as well as a JFET. :lol:

 

[_3iMaJ]

might be able to do it with an AGC (automatic gain control) circuit somewhere in this path. You can allow maximum signal to top out without clipping.

Absolutely! Thats immediatly what I thought when I read this post. An AGC will normalize your signal to some nominal power level. Think smart sound on your TV, this will work wonderfully for your application.

 

[zachtheterrible]

Reading through this, I couldn't help but ask: why not just use a 10k audio POT? POTs don't clip an audio waveform, they just decrease the amplitude of the entire signal don't they?

 

[_3iMaJ]

Reading through this, I couldn't help but ask: why not just use a 10k audio POT? POTs don't clip an audio waveform, they just decrease the amplitude of the entire signal don't they?

If you use a POT you'll be constantly adjusting it depending on the amplitude of the music. If you use a different method such as an AGC you won't have to make any adjustments to it once you've installed it.

 

[mstechca]

Nigel will probably mark this idea as crude, but here it is:

Now get yourself a counter. a 4040 CMOS counter will do. Now get a whole bunch of 10K ohm (or so) resistors Connect one resistor to Q0. Tie two resistors together and connect them to Q1. Tie 4 resistors together and connect them to Q2. Now you have 3 hanging points. Tie them to the output where the speaker is connected, not to ground.

What you have is a counter which will go from 10K to 70K in 7 steps. Basically, the lower the resistance, the lower the volume.

For a finer tume, lower the values. Don't go under 1K.

It is just a thought. I'm not sure if it works for your application.

 

[Roff]

Nigel will probably mark this idea as crude, but here it is:

Now get yourself a counter. a 4040 CMOS counter will do. Now get a whole bunch of 10K ohm (or so) resistors Connect one resistor to Q0. Tie two resistors together and connect them to Q1. Tie 4 resistors together and connect them to Q2. Now you have 3 hanging points. Tie them to the output where the speaker is connected, not to ground.

What you have is a counter which will go from 10K to 70K in 7 steps. Basically, the lower the resistance, the lower the volume.

For a finer tume, lower the values. Don't go under 1K.

It is just a thought. I'm not sure if it works for your application.

mstecha, we have tried to explain to you that 4040 outputs don't switch between open circuit and GND. They switch between open circuit and VCC. When you post rubbish like this, you are not helping the OP. You are just confusing him.
Edit: This was supposed to read "They switch between GND and VCC".

 

[zachtheterrible]

Ohhh, didn't realise he was looking for AGC. Just thought he wanted to lower the volume :lol:

 

[audioguru]

4040 outputs don't switch between open circuit and GND. They switch between open circuit and VCC.

Actually you are both incorrect. The outputs of a 4040 counter switch between VCC and ground. They are never open circuit. :lol:

MStechca's hair-brained idea wouldn't work even if the counter provided switched resistors:
1) The output resistance of the counter is about 200 ohms.
2) Seven 10k resistors in series with the outputs and all in parallel produce 1.5k.
3) Since when is a speaker signal reduced if 1.5k or more is added in parallel with the speaker? :?: :?: :?:

 

[Roff]

4040 outputs don't switch between open circuit and GND. They switch between open circuit and VCC.

Actually you are both incorrect. The outputs of a 4040 counter switch between VCC and ground. They are never open circuit. :lol:

MStechca's hair-brained idea wouldn't work even if the counter provided switched resistors:
1) The output resistance of the counter is about 200 ohms.
2) Seven 10k resistors in series with the outputs and all in parallel produce 1.5k.
3) Since when is a speaker signal reduced if 1.5k or more is added in parallel with the speaker? :?: :?: :?:

OOps! That was a brain fart. I meant to say "They switch between GND and VCC". If you look at my post here, it illustrates what I intended to say.

 

[Sebi]

You need an automatic level control...

 

[Dr.EM]

Precisely! Although this may work better as a limiter:

**broken link removed**

 

[audioguru]

If cassette tape recorders were still made, then a semiconductor company would still be making an audio limiter IC.

AGC wasn't asked for in this thread. Just a simple method to limit the power to headphones. High-power amps limit power to headphones with simple series resistors, so why can't they be used for this requirement?
Two more resistors might be needed to make voltage dividers if the headphones are high impedance, but won't affect the reduction for low impedance ones.

With a second thought about limiting power with simple resistors, just think of the lack of headroom causing the user to "crank up the volume" so the source clips all the time! Horrors, it will be as bad or worse than having hard limiters. :lol:

 

[Nigel Goodwin]

If High-power amps limit power to headphones with simple series resistors, so why can't they be used for this requirement?

Because they don't "limit" the power, they simply reduce it. I'm presuming he's wanting something to help reduce the possibility of hearing damage whilst using headphones?. Reducing the possible power with resistors will only work for a specific signal input level, or by reducing the level so far that the volume will be running full out all the time, and it's still too quiet.

Personally I'd just say "don't turn it up too loud!".

 

[audioguru]

While shopping, I frequently hear a kid's earphones before I can see the kid! In a crowded space like an elevator or something, the sound from the earphones is deafening to me, what about for the kid wearing the earphones?
I suppose the kids with their earphones so loud are already deaf so need it louder. Acousic and deafness runaway. :lol:

 

[Dr.EM]

Yeah, i've seen/heard this. It must be really painful to be honest :lol: