How to Make Voices or Audio Sound Like a Radio in Audacity
To make voices sound like are coming from a radio is really simple in Audacity. Using a combination of the Equalization Effect and a High Pass Filter you can create realistic radio-sounding audio.
Select your clip. Go up to the Effect menu and click Equalization. Make sure you are in the Draw Curves mode at the bottom left. You only need 2 points on your curve. First click a point approximately at 1,000 Hz (on the bottom) and 12dB (on the left). The entire line should move up. Then click at around 10,000Hz and and -12dB (negative). Press OK and the waveform of you clip should amplify.
The second thing to do is to apply a High Pass Filter. Click Effect and go down to High Pass Filter. The settings should be Rolloff: 6 dB, Filter Quality: 0.7 and Cutoff Frequency: 2,000.0 Hz.
You can repeat the steps for a more radio-sounding effect but thats pretty much it.
If youre not sure, Audacity is a great free audio editing software. Its open-source and virus free.