Trouble with Frequency Modulation

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Trouble with Frequency Modulation

Postby Apno » Thu Jul 06, 2017 10:37 am

I'm have amplitude problems using the FM effect in the Expression Evaluator. It always clips the signal to be modulated.
For Example: A file with a 3000Hz sine wave, peaks at -6dB. Use EE and apply FM at 11Hz. Now the signal is slammed right up to 0dBFS. It does not matter what the level of the signal being modulated is, the result is always pushed all the way to 0dB and smashed at the peaks. I've tried altering some parameters, but so far nothing helps.

cos(2*pi*f*t + y*wave(n))

Any ideas here? First I'd like not to smash the signal against the 0dB roof, and second it would be nice to control the depth of modulation.

Thanks!
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Re: Trouble with Frequency Modulation

Postby DougDbug » Thu Jul 06, 2017 2:37 pm

I hate to admit it, but I don't understand how that expression "works". And, I'm at work right now so I don't have the time to figure it out...

But I do know that cosine can evaluate to 1.0 (=100% =0dB). And, I assume you know that each sample represents an amplitude and each expression-evaluation of a sample is a new sample amplitude[/b].

You can apply [i]maximize Volume
after frequency modulation to set a new peak level of your choosing.

and second it would be nice to control the depth of modulation.
With FM the "depth" of the modulation is the amount of frequency modulation, which I assume is 'f'.

...With FM radio "100% modulation" is defined legally as the amount you're allowed to deviate from your assigned center-frequency. And the amplitude is constant, again legally determined by the maximum transmission power allowed with your particular broadcast license.



P.S.
Maybe we've (I've?) got this 'backwards"... Maybe it is like FM radio where we're generating a constant full-volume tone (which in radio would be the broadcast frequency), and modulating that tone with the WAV file as the "signal".
Last edited by DougDbug on Thu Jul 06, 2017 3:01 pm, edited 2 times in total.
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Re: Trouble with Frequency Modulation

Postby Apno » Thu Jul 06, 2017 2:47 pm

Thanks Doug. Yeah, after I posted I thought better of that "depth of modulation" request. :oops: That works for AM, not for FM.

If you get a chance, take a look at what the FM preset does. You'll see that no matter what your staring level is, the result is pushed up and compressed to 0dB. So it adds a lot of distortion to the modulated waveform. I'd like the original signal not to peak or compress, but so far have had no luck. I can make it worse, but never better.
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Re: Trouble with Frequency Modulation

Postby GoldWave Inc. » Thu Jul 20, 2017 9:51 am

Frequency modulation is full scale, which means the carrier signal amplitude always goes from -1 to +1. The distortion is not a result of the full scale amplitude. The distortion is the frequency modulation. Perhaps you are looking for a Tremolo effect instead.
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Re: Trouble with Frequency Modulation

Postby Apno » Sun Aug 06, 2017 5:28 pm

Yes, tremolo is closer to what I need and I've been working on tweaking that. Thanks!
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Re: Trouble with Frequency Modulation

Postby kajol » Wed May 15, 2019 6:30 am

if you get a risk, test what the FM preset does. you will see that irrespective of what your staring degree is, the end result is driven up and compressed to 0dB. So it adds loads of distortion to the modulated waveform. I'd like the original signal now not to height or compress, however to date have had no luck. I can make it worse, but in no way higher.
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