Audio Leveler

mikkut

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I recall this being brought up a few times over the years but I don’t think I ever saw a practical solution. Is there a device that you can run audio through that will level widely ranging incoming audio levels? I have this issue on all of my scanners but it is particularly bad on the SDS 100/200’s. Some transmissions come in that you can barley hear and others come in so loud that the sound completely over modulates, all with the volume set at the same level. I’m guessing this is not an issue with the scanner but rather it has something to do with the radio systems I’m listening to since this issue frequently occurs with different radio I.D.s on the same TG’s. That also means the +/- 3 audio offset feature doesn’t work for this. Hoping there is something new out there for this ….
 

Ubbe

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There's no audio AGC in the SDS scanners. I don't why it was removed as it has its use in older Uniden and Whistler scanners. There's compressors for studio work that can be used. They are something like $75 and up. Search Ebay for "compressor / limiter". You connect the scanners earphone jack to the compressor and its output to either your computers line in or a pair of amplified computers speakers. The compressor have limiters and adjustments for different timings to make it react slow or fast to the signal, whatever sounds best to your ears.

/Ubbe
 

ratboy

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I really need to find something like that for my two SDS200's. There are a couple of things I want to listen to that are like 5 times louder than anything P25 on the radio. The level adjustment doesn't even come close. Around dawn every day, it comes to life and I have to turn it down to the point I can't understand much else to be able to tolerate it.
 

bharvey2

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I second Ubbe's suggestion of a compressor/limiter. The audio/recording world has used them for years and the variety is staggering. With the proper one, you could have a pre-compression gain stage to bring up your low volume signals. For scanner listening, you don't need one with a wide frequency response. If you have a computer with a decent sound card, you might be able to find some compressor emulation software in an audio recording package. An old, free one is called Audacity.
 

majoco

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Some time ago there were kits using the Plessey SL6270 IC that supposedly worked well but I haven't seen one lately.
 

RFI-EMI-GUY

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Device description via contributor, Jay in the Mojave.

See his posts & threads here and elsewhere.

Several other good ideas floating around it. (On RadioBanter, IIRC)
well that is dirt simple. does it work?

 

slowmover

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Post #9 link. There’s more on the RR site and elsewhere.

(No, I haven’t built it yet.)

.
 

Ubbe

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It's a 6.3volt 1watt light bulb. Light bulbs have low resistant when cold and high when lit and warm at about a 1:4 ratio. Put a light bulb in series with a speaker and if the voltage and wattage are correct the light bulb will light up at higher volumes and drop the signal level to the speaker.

If you put a potentiometer over the light bulb, they suggest a 25 ohm one, and wired so you can adjust it from 0 to 25 ohm in parallell to the light bulb, it could be used to set how much the light bulb should reduce the sound level. It is very dependent of the impedance of the speaker so other light bulbs might be needed to adapt to a certain speaker.

A 6.3v 1watt bulb have a 40 ohm resistance when lit and probably 10 ohm when unlit. It probably differ between different brands of bulbs. This is probably a very old type of the General Electric brand GE-47 bulb and modern ones might not have that low resistance when cold as low resistance will create a current surge that lowers the life of a bulb and they might now have different volfram materials.

/Ubbe
 
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slowmover

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It's a 6.3volt 1watt light bulb. Light bulbs have low resistant when cold and high when lit and warm at about a 1:4 ratio. Put a light bulb in series with a speaker and if the voltage and wattage are correct the light bulb will light up at higher volumes and drop the signal level to the speaker.

If you put a potentiometer over the light bulb, they suggest a 25 ohm one, and wired so you can adjust it from 0 to 25 ohm in parallell to the light bulb, it could be used to set how much the light bulb should reduce the sound level. It is very dependent of the impedance of the speaker so other light bulbs might be needed to adapt to a certain speaker.

A 6.3v 1watt bulb have a 40 ohm resistance when lit and probably 10 ohm when unlit. It probably differ between different brands of bulbs. This is probably a very old type of the General Electric brand GE-47 bulb and modern ones might not have that low resistance when cold as low resistance will create a current surge that lowers the life of a bulb and they might now have different volfram materials.

/Ubbe
Define “modern”. A dozen years back (guesstimated) isn’t old.

.
 

Ubbe

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Isn't 6,3v the voltage for the heat filament of electron tubes, so perhaps from the era when tube radisotations where very common and a light bulb where indicating on the rig that the heat was switch on to the transmit tubes.

/Ubbe
 

slowmover

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Isn't 6,3v the voltage for the heat filament of electron tubes, so perhaps from the era when tube radisotations where very common and a light bulb where indicating on the rig that the heat was switch on to the transmit tubes.

/Ubbe
That question is brought up elsewhere. I’d do the recommenced Net-wide search for Jays comments (and others responses).

He notes this was popular in SSB use in the 1970s (as the starting comment).

Others bring up alternative views and solutions.

.
 

Ubbe

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That question is brought up elsewhere. I’d do the recommenced Net-wide search for Jays comments (and others responses).
Galaxy 86V "The Stryker 955 audio output feeds to two diodes back to back to eliminate the audio spike heard when keying the mic, then goes to a old Sonic Cushion a GE47 light bulb across the audio wires, then feeds a 25 ohm pot, this significantly levels out the audio volume on SSB, then the audio is sent to a Clear Speech DSP Filter (Digital Signal Prosser) and the DSP really helps to clean up left over noise."

Silicone diodes have a conducting voltage of 0,7volt and putting two back to back on the speaker wires will reduce the level to 1,4volt peak-to-peak, a very low volume, and higher outputs will act as a short circuit to the audio amp. Maybe it will work better with tubes, and a high impedance to low impedance transformer that all tube speaker amplifiers use, without destroying the amplifier. Having a light bulb across speaker wires makes no sense. He probably doesn't understand how it actually works. I often find that to be the case when CB guys discuss technical matters.

/Ubbe
 

RFI-EMI-GUY

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Here is a standard application of a light bulb as an AGC device. Commonly used in an HP200A Wein Bridge oscillator that made HP rich and famous. Motorola likewise used a light bulb in the audio amplifier of some very early dispatch consoles.


The interesting part about the light bulb is that although it has a very nonlinear amplitude response at low frequencies, it introduces little distortion at audio frequencies. Weird...
 

RFI-EMI-GUY

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I wonder how something like this might work for this application? On one hand the P25 audio levels vary wildly, on the other hand the content is already quite compressed suggesting that expansion might help.

Alto-Quad-Compressor-Limiter-CLE-4-0



dbx 166A Compressor - Limiter - Gate
This has an expander...

 
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Ubbe

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It shouldn't matter if the audio are already compressed. You always have a limiter that you set to take care of sudden peaks in the audio and that will be virually unused with already compressed audio sources. The speed of the attach and release of the compression are set to get the most pleasent audio without creating a too much pumping effect. Some very cheap compressors lack som adjustable controls like attack time or even release time that are needed to tailor the sound to your preference.

/Ubbe
 
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