Volume (decibel) Low-pass filter (NOT frequency filter)

Hello, I need a circuit for building a volume low-pass filter. why? The problem is that every time there is a commercial on TV they increase the sound level. I want to combat this by building a maximum sound cap limit (adujstable via Pot.). It should work on all frequency and should not reduce sound for any db lower then the cap limit. Now the best version of this is that the cap is automaticaly based upon the avarage volume, so this will work in every sound levels (meaning cap = normal sound+10db, for example). But it this is too complicated then a fixed cap with pot. will be enough.

Since I have only very basic knowledge of electronics, a reference to a detailed site will be nice. Thank!

Reply to
KeeperOfLogic
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The device you need is called a limiter, which is a special form of compressor. (The term 'limiter' is used for lots of other circuits; this one is specific to audio.) These are (or used to be, anyway) standard devices around recording studios. The basic idea is that the circuit monitors the average volume and if that exceeds the preset limit it starts applying gain reduction to keep it at the limit.

There will be a tradeoff between speed of operation and audible artifacts like distortion. You don't want to have it react so fast that it clips individual peaks, or you will have horrid distortion. But if you set it to react too slowly, there will be overshoot and "pumping" effects. A typical approach is to make the release time longer than the attack time to help reduce the pumping.

Best regards,

Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis

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Reply to
Bob Masta

=============================================== One brute force way of achieving this goal (probably suitable only for rich TV watchers) is to hire a carbon based semi intelligent volume control technician that adjusts the audio gain up and down during commercials to match the boss's desired psychoacoustic reference level.

Reply to
BobG

Some information to supplement Mr. Masta's answer can be found at Wikipedia:

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Unfortunately, a hardware solution isn't going to happen at the hobbyist level -- limiters are complex and expensive pieces of equipment (otherwise we'd all have them).

Cheers Chris

Reply to
Chris

Remote control with "mute" is the only practical answer.

You could build up a peak detector or an average detector or an rms detector (each getting more involved, from left to right) and still find that falsing and failure to trip problems would drive you nuts.

Reply to
Charles Schuler

Thank you all for your comments. I thought that if freq. filters are so easy to made, then volume shouldn't be a problem. But I see that there is a consensus among you about the ineffectiveness of building one. I still think this circuit should be implemented inside TVs ;) If you are so helpull, could you also help me with something that

*should* be very simple as well ? I want to connect a LED to my audio cable, that should light stronger as volume increases, simliar to equalizer - when you hear a shot sound for example, the LED should flash for a sec. I've seen solutions with several LEDs and band-filters but I only want one LED. Any thoughts?
Reply to
KeeperOfLogic

I'd go for a duty-cycle circuit where the on-time of the pulses to the LED increases as audio volume increases.

Reply to
Charles Schuler

what you want is called a "compressor", It's a rather complex project, maybe you can find a kit somewhere?

Bye. Jasen

Reply to
jasen

There was a "commercial detector" circuit once - might be worth a search.

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Reply to
Homer J Simpson

On a related idea, I noticed many years ago that commericals on standard FM radio tended to be broadcast in mono, whereas music was in stereo. My thought was to compare the L and R channels and if they were the same, apply muting. This never really got off the ground, since I would have to allow for simple gain differences (balance at the receiver or mismatch in recording, etc). Plus, all music could be expected to have some passages that were mostly mono, so there would need to be some "smarts" and time delays. Nowadays with DSP methods this might be more approachable, but I wonder if commericals (radio and TV) are now all in stereo anyway... Just a thought!

Best regards,

Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis

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Home of DaqGen, the FREEWARE signal generator

Reply to
Bob Masta

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