Record static sound effects

March 7, 2017
Sunday Sound Effects Round Up

I feel your choice of plugins might get you near the sound you want to hear in your song (heck, they might even get you somewhere better!) but as for recreating the distinct sound of AM radio (specifically AM TALK radio)... well, I'll just say that your way seems like WAY more work than it needs to be and start with the explanation.

Before we start recreating "the AM sound" we should take a second and define what the differences we are trying to recreate ARE. It's obvious that it sounds DIFFERENT but what are those differences? Well, people usually say that FM radio sounds both cleaner and brighter than AM... when they say cleaner, they usually mean that AM is more "static-y" and FM isn't but if you removed all the static I'd be willing to bet they'd still say FM sounded clearer and brighter than noise-free AM signal. This is because the "AM talk radio" sound is due entirely to AM radio stations' baseband being limited to 5kHZ of bandwidth where FM stations' baseband is limited to 15kHz. Neither are large enough to include the full range of human hearing (15Hz-ish -> 22kHz-ish) which is why FM doesn't sound like a CD but more like a 128-192kbitrate mp3.

In all that I said two things- that I don't think a simulation of static is necessary (or desired) to get the "AM sound" that you want and There are two detectable ways in which noise/interference/static-free AM sounds different than FM- they have been termed "brightness" and "clarity" and ARE seperate differences, yet they have the same origin- 5kHz of signal vs 15kHz of signal. (I say 5kHz instead of 10kHz which is what AM is really allocated by the FCC, but we are gonna call it 5Hz for a reason that I may or may not get into; I just didn't want to give bad info.)

Have you ever listened to AM talk radio stations on XM or Sirius radio? Noticed that they sound WAY different? To me, it sounds like no matter how loud I turn it up, I just can't quite make out some of the things they said. If you flip over to the same broadcast on actual AM radio the difference between the two will be immediately apparent- it's like on XM radio, an AM talk radio broadcast is lopped off on both ends of its frequency range and it's this little stream of signal lost in this big range of "empty frequency" its been mixed with and the empty frequencies fill the space at a cost to overall volume. But I digress...

According to the FCC regulations of AM radio- "Emissions 10.2kHz to 20kHz removed from the carrier must be attenuated at least 25 dB below the unmodulated carrier level". Above 20kHz the attenuation keeps ramping up and the FCC quote about it was long enough to require paraphrasing. ;)

What this boils down to for us is that since they start lopping off the AM signal by turning down the volume 25dB over 10k->20kHz, in the interests of maintaining a loud signal most AM talk radio broadcasts lop off everything above and below a 5kHz-ish sized width of band. Therefore all you should have to do is resample your audio at a lower rate- somewhere between 5kHz and 10kHz is about right... also, I would suggest doing it this way in Soundforge; that's what I'm thinking of as I write this- SF even calls one of its resample presets "radio quality". However it's really quite a basic thing so while I'm certain there are many programs that will do it (bitcrusher does it but it also does more stuff to get its sound so it might not sound right) I can only really speak for the audible results of doing it in SoundForge... I'd go out on a limb and say audacity as well, but there's a WORLD of difference in how their normalize function ends up sounding so maybe they can screw up resampling, too. :)

Or, of course, you could attenuate the signal 25dB for the freq range of 10.2-20k, maybe 35dB for 20k-30k and then 50dB+ above 30k. Or just half the volume of 10k-20k and cut the rest.

Additionally, you could always use two smartphones; one to play the audio on speaker and one to record it with the mic of the other phone. Two iPhones would work superbly, as would many Androids as well.

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