movie automatic volume control audio compressor

Sometimes you need to automatically adjust audio-volume or gain, for several purposes. The first time in my case to perfect the modulation depth of a (HAM) amateur transmitter, but later for more than that. To keep the neighbors’ happy, I cannot watch movies late in the evening. And do not forget music…!
Most of the movies i see on tv or computers, contains audio mixes mend for large auditoriums and theaters. There is an enormous difference between the dialogues, the music and effect sounds. To help average the differences, automatic gain adjustment comes in handy. In the past i build a unit with transistor or fet as active attenuator. Not all that good, little distortion but did the job.
Until I read an article about the strange behavior of diodes, when used below their threshold. You can alter the resistance by applying a small current. I experimented out of curiosity. But before I know it, build a complete stereo gain control with compressor and limiter. From parts out of the old stock or junk box.

[@DXCommanderHQ]

I just watched your video on the VHS audio project. Superb work my friend. What a fabulous engineer you are! I used to have a lof of fun with VHS also. Great fun. 73, Callum.

[@TheoFaber]

Thanks! en ook 73 voor jou! (PA2THF) Theo.

[@skitliv]

Great video, very interesting. Thanks! Hope all is well. Cheers from Sweden

[@TheoFaber]

Thanks, all the best to you to!

[@weistonaski6924]

Thank you for putting those on youtube, there's lot of knowledge into those schematics and explanation and i value this. Also you're accent and wording is pefectly fine to understand and i really like the contrast between your voice and the generated female voice wich make the video feel like a documentary (that and the zoom in / zoom out thing) I still don't completely understand the diodes as potentiometer so i suppose you could have highlighted this (i will take more time to look at the schematics)

[@TheoFaber]

Thank you for the nice words. My accent is Dutch (The Netherlands). A potentiometer has a variable resistance. In this case, the higher the Voltage (current) throe the diode, the lower it's resistance. So the resistance of the diode, is not constant, like a potentiometer. The phenomena only happens, before the 0,7V (by this diode) is reached. Above this value resistance is almost constant.

[@robvdc]

Hallo, voor een FM-geluidszender in huis uitgaande van een paraboolontvanger, gebruik ik een eenvoudiger circuit waar ik al jaren voldoening uit haal. Dit is een schematische kopie van een ALC van een cassetterecorder uit eind jaren 70. Houd de ingang resistor hoog om distortion te voorkomen. Hallo uit Luik België 🙋‍♂️

[@TheoFaber]

Hoi Rob - had je er een schema bijgedaan? ik zie niets.

[@HappyQuailsLC]

I need an external fader inline to my Tape Line In

[@SPINNINGMYWHEELS777]

what are the downsides using this application with the diode stages vs more traditional shunting / compressing circuits? My question comes out of the idea can it be used in a professional recording application or is it just suitable for casual listening? For instance can it handle an audio signal of more than 22khz per channel without distorting?

[@TheoFaber]

Yes it can handel 22kc without any problem. The resistance of the diode's are almost linear, so i see no reason why it good not function in a pro appl. But now-days there are so many options available in any pro store.

[@SPINNINGMYWHEELS777]

@@TheoFaber thank you for taking time to reply and your efforts . Great fact based channel . Why did you turn the comments off the VCR / VHS to Audio recorder? I hope no one was giving you a hard time friend.

[@TheoFaber]

@@SPINNINGMYWHEELS777 Yes they did. Mostly because they do not watch more than 2 minutes. I explained several times that the design was from 1982. But still they ask why i not use 2023 equipment? And another guy had remarks about my English. I explained that I am Dutch so it's sometimes difficult. I get the answer that again there where som words with faults in them. I only made a short film about my projects, that are for 90 procent just hobby and to investigate something. It's a strange world. And I do not know WHY in a few day's there are so many viewers???? (30.000)?

[@pierrebladt4547]

Is het mogelijk om het schema te ontvangen en eventueel een pcb layout?

[@TheoFaber]

Ja hoor, schema wel, pcb is nooit getekend helaas. Stuur maar een pb met je mail-adres; stuur ik het naar je toe!

[@sjoerdbalfoort7170]

mijn vraag als absoluut "null" op electronica gebied...... werkt Dolby C ook niet op zo'n principe? maar dan in frequentie uiteraard...

[@TheoFaber]

Dus zo'n nul ben je nu ook weer niet. Inderdaad een beetje is dat zo. Het audio (Dolby C) wordt opgesplitst in div frequentie bandjes en apart bewerkt. Maar wel met 'vaste' versterking en demping. Bij dit doosje, ligt de nadruk op compenseren van volume verschillen. Dus alle frequenties in 1 keer. Met name bij de vele films die ik heb en afgemixt zijn voor bioscoop.

[@sjoerdbalfoort7170]

@@TheoFaber is wel wat voor mij dan. Ik ga niet meer naar de grote bioscopen vanwege het geluid. Een ontploffing is hard maar verdraagzaam maar de acteur die daarna wat schreeuwt klinkt net zo hard en die frequenties zijn bijna pijnlijk...... om maar een voorbeeld te noemen en dat probleem heb ik dus thuis ook......vandaar.

[@TheoFaber]

@@sjoerdbalfoort7170 Ik ga (bij uitzondering voor spektakel films) nog wel naar 'grote' bioscopen, maar heb dan altijd oordopjes bij me. Meestal kijk ik ze gewoon thuis. Ga wel zeer regelmatig naar de 'betere films' en die draaien gelukkig in filmhuizen, waar het geluid nog als vanouds staat. Vaak Bussum of Hsum, maar soms ook Studio K enz. Voor mijn eigen kamer heb ik nu dit doosje met veel plezier. Helaas bestaat er maar 1 exemplaar van...!

[@SPINNINGMYWHEELS777]

my dolby swtich is always broken 😎

[@mediair2007]

Too tecnical for me 😱 but sounds like there are new possibilities....

[@TheoFaber]

If you love your neighbor's, it's a must have....🤫

[@hugoromeyn4582]

@@TheoFaber It's also a must have when you love your loudspeakers more than your neighbors 😜

[@SPINNINGMYWHEELS777]

@@TheoFaber my neighbour lives across the acres of field :) I also don't watch movies anymore either. Got sick of the 'classics' .. too much propaganda in movies now and they are terribly contrived and too much digital garbage on screen.

[@MePeterNicholls]

Do you know Optimod? I think this is how their analogue auto gain works

[@TheoFaber]

No I don’t. Was reading about diode behavior below there threshold value. So I tested this, and indeed - below 0,7V there resistance depends of the voltage. It seems a linear process and before I new it - i build several component around it. Because it was so much better that what I experienced with transistors / fet’s, I made this unit. Use it every day, whenever I play-back a movie!

[@MePeterNicholls]

@@TheoFaber orban is the company, Dutch I think too. Broadcast auto gain, compression , limiting. For tv radio digital. Current gear is mostly digital now, but their older analogue gear is very interesting

[@TheoFaber]

@@MePeterNicholls Thank you for the info! But i am more of a technician and wanted to investigate the working of the diode in circumstances beone there normal use. By testing and measurement it get out of hand, the positive way. I am happy with the outcome and use the unit constantly.

[@MePeterNicholls]

@@TheoFaber oh yes I can appreciate that! “Rabbit hole” syndrome

[@Sector-xNl]

You can save yourself a lot of trouble by simply purchasing a television, receiver, soundbar, etc. with a built-in compressor/limiter. No matter how ingenious this diode based contraption works, it works analogously and can therefore not be used everywhere.

[@TheoFaber]

You are missing the point. It's just a hobby to experiment with electronics an to learn something. It has nothing to do with what is economical or simpler. But thanks for the response!

[@Sector-xNl]

@@TheoFaber Oh sorry Theo, in that case, I must apologize myself. Of course, it's fun and interesting to experiment, learn, and discover things. I didn't see it that way. Have fun and good luck with your hobby.

[@pierrebladt4547]

Pb gestuurd

[@TheoFaber]

Heb je het schema nu ontvangen? Dacht het gestuurd te hebben, maar kan het hier niet terugvinden? dat berichtje...

[@pierrebladt4547]

@@TheoFaber ja hoorvia messenger