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St3venhall

Member
Joined
Aug 12, 2022
Messages
5
Location
CLAREMONT, NH
Hello everyone! This is my first post so I hope I'm not breaking any rules.

I am looking to build an inexpensive audio compression/limiting circuit using a 3.5mm headphone Jack as the input and 3.5mm for the output as well. It will need to be passive, or maybe battery powered but I would really prefer to have it be passive, if possible.

For the compression I'm looking for a very high ratio limiter, with fast attack and fast release. Basically my objective is to squash the audio input and normalize it without clipping, the threshold should capture just about every audio input signal, excluding the noise floor (static, etc.).

This is not for music applications, the overall objective is to take whispers and screams that might be in a podcast or something and have it all come out at the exact same level. I want to eliminate any dynamic range from the audio source.

I'm a novice with electronic DIYer with an audio engineering degree, and have arduino's and a couple of component kits, etc. I know I will probably need some special transistors or maybe an IC chip, but information on the Internet is very scattered. Does anyone have any ideas or possibly resources I could turn to?

Thank you so much!
 
Passive and high ratio limiter do not really go hand in hand so I think you will have to settle for a batter y operated device. As this seems to be primarily for speech I would suggest you search the amateur radio and CB sites because they often use basic compressor/limiters to improve intelligibility over long diatances.

Cheers

Ian
 
You're not breaking any rules but I'm pretty sure you're trying to break the laws of physics.

If the device is passive, you cannot have voltage gain unless you use a transformer. But transformer voltage gain comes at the cost of current. And I don't think you can have a feedback mode compressor because if you put the transformer after the series resistance, you don't have the power to drive it. Also, you're only option for an attenuation device would be maybe a mosfet because it's off when biased to 0V. In theory you could step up with a transformer and bridge rectify with some diodes to make a bias for turning on a mosfet shunt. But even if this could be made to work, it would probably be a very crude device and nothing like the characteristics you seek.

Even if you used a powered device, achieving the paraticular set of compression characteristics would be difficult. It would require a PCB with many components. It's just not a battery operated device.

If you're just doing podcast stuff, maybe look for a software plugin.
 
There are quite a few passive compressor designs around. Most consist of a pot divider made from a series incandescent bulb and a resistor to ground. The cold resistance of the bulb is low. As the signal increases the filament heats up and its resistance increases thus dropping the output level. The downside is you ready need to drive them from a power amp capable of supplying a few watts.



Cheers

ian
 
Thank you everybody! Well, from the information it looks like going passive is not an option. I'd be willing to maybe plug it in through micro USB if that would help give me the power I need for this kind of compression? I know some of the things you guys are saying seem simple but all of the information you have provided is helping a lot! I'm excited about this project, but the low/medium threshold + high ratio and gain control is important. Any other ideas? Maybe a amplifier in the circuit?
 
It seems the first question to ask is: "How high is you input signal level?"

I tried the Elektor circuit Tekay suggested. It works fairly well provided you drive it with a healthy line level signal. And you can allow for some distortion. Something tells me you're looking for a compressor that goes between a microphone and a preamp?
 
It seems the first question to ask is: "How high is you input signal level?"

I tried the Elektor circuit Tekay suggested. It works fairly well provided you drive it with a healthy line level signal. And you can allow for some distortion. Something tells me you're looking for a compressor that goes between a microphone and a preamp?
Well, the input signal will vary- a lot. It's not for a microphone setup, no. Imagine the device recieving it's audio from a TV show, straight out of the televisions headphone or AV jacks. That is what I'm looking to compress. I'm realizing now that the input level would vary due to the televisions volume setting as well... I wonder if there's a way I could get that audio "pre-volume" from the device... hmm... Thanks again!
 
If the TV has a line out, that would be less of a problem. Of course, not all TVs have an analog line out...
 
For leveling of a TV signal, the best way is to make a compressor that has a 2:1 ratio, and then boost the input until it is on the middle of the range. Then adjust the output to a good level. It basically reduces the dynamic range in half, but still has dynamics.
 
For leveling of a TV signal, the best way is to make a compressor that has a 2:1 ratio, and then boost the input until it is on the middle of the range. Then adjust the output to a good level. It basically reduces the dynamic range in half, but still has dynamics.
Thank you! Now I just need to figure out the circuitry...
 
I am looking to build an inexpensive audio compression/limiting

For the compression I'm looking for a very high ratio limiter, with fast attack and fast release.

overall objective is to take whispers and screams that might be in a podcast or something and have it all come out at the exact same level. I want to eliminate any dynamic range from the audio source.

Like others have said,
if you are doing a Podcast or similar a Compressor/Limiter software Pluginb would do what you need quite well.

Why don't you use a computer plugin?
 
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