[ASTERISK-6] Resonant Filter To Simulate N-Carrier

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Resonant Filter To Simulate N-Carrier

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Details

Category: Asterisk
Type: New Feature
Severity: Trivial
Visibility: Public
Reported: 3/22/2022 11:46 AM
Last Active: 5/21/2022 7:01 PM
Status: Resolved 7/26/2022 10:05 PM
Reporter: KurisuYamato
Watching: KurisuYamato
Assigned To: Nobody

It has been discovered that, if used properly, a Resonance Filter applied to voice communications can create an effect very similar to the resonant properties of Bell System N-Carrier. In particular, if a wet-dry signal mix is kept at a moderate to high level with a frequency set to 3700 hz.

Thus it seems possible that a real-time option in Asterisk to apply such resonance to a channel can be added and implemented to great effect.

A candidate written in C has been found here: https://www.gamedev.net/reference/articles/article845.asp -- it should be noted that this is a "low pass" filter, but based on my current understanding of N-Carrier and my testing with resonance filters on other audio the behavior of a low pass filter seems ideal for this purpose.


Comments

5/17/2022 5:11 PM — InterLinked

Give this a try when you get a chance and let me know how it works for you: https://raw.githubusercontent.com/InterLinked1/phreakscript/master/funcs/func_resonance.c

It definitely seems to have the right kind of impact on the audio, thought maybe it sounds somewhat "dirtier" than if you were to do it in your audio program on an audio file.

5/17/2022 9:57 PM — KurisuYamato

It's a very subtle effect but it is there. I was honestly expecting an initial test to result in a wash of resonance audio.

It does indeed have a "dirty" quality to it. While 3700 is the ideal "test" frequency, I may do well to try some other frequencies, possibly harmonics of 3700 which were present and more prominent in carrier noise to see how those sound.

It's certainly something to experiment with.

5/21/2022 7:01 PM — Southernphoneman

Yes will give it a looking at thanks

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