Which part of the chain does most of the work?

The high pass. Losing the low end is what gives the sound its small-speaker quality, and it is usually more recognisable than the loss of high frequencies. The midrange boost and the steep low pass complete the impression, but the thinness comes first.

Why is the low pass applied twice?

Because a single stage gives a gentle roll-off that sounds like a tone control, whereas two cascaded stages produce a slope steep enough to sound like a band edge. The measured figure is about eighteen decibels down an octave above the corner, which is what makes the band sound closed.

What is the drive stage for?

It adds harmonics of the surviving signal, which is how an overdriven transmitter or a small speaker behaves. Without it the result would be a filtered signal, which reads as equalisation; with it the effect sounds like a device rather than like a setting.

Why does the effect not include static?

Because the target is the voicing of a receiver rather than its faults. Adding crackle and interference would be a different effect, and if a noisy transmission is what is wanted, the vinyl record effect supplies surface noise and crackle of exactly that kind.

Do the two voicings sound very different?

Mostly in bandwidth. The AM setting stops at three thousand two hundred hertz, which is obviously narrow, while the FM setting keeps most of the audible range and reads as a clean broadcast. The midrange boost and drive figures differ too, but the bandwidth is the dominant difference.

Radio Effect

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Radio Effect narrows a recording to the frequency range a broadcast receiver passes and adds the saturation that comes with it. Two voicings cover the AM and FM characters, with a tone control over the midrange.

What is Radio Effect?

Drop a file, choose a voicing, set the tone tilt, and process; the chain applies a high pass, a midrange boost, a steep low pass and a drive stage in that fixed order.

The controls and the chain:

A voicing choice between an AM patch and an FM patch.
A tone control from six decibels down to six up, which tilts the midrange of the peaking stage.
The AM patch uses a highpass at two hundred and fifty hertz, a lowpass at three thousand two hundred, a midrange peak at fifteen hundred boosted ten decibels, a drive of three and a half and a make-up of minus six decibels.
The FM patch uses a highpass at eighty hertz, a lowpass at eleven thousand, a midrange peak at twenty five hundred boosted three decibels, a drive of one and two tenths and a make-up of minus three.

The chain is the effect, and the order matters. The high pass removes the low end that a receiver could not reproduce, which is what gives the sound its thin, small-speaker quality and is a larger part of the character than the low pass is. The peaking stage then lifts the midrange, where a small speaker is most efficient, which is the nasal quality that listeners associate with radio. The low pass is the other edge of the band, and it is applied as two cascaded stages rather than one, giving a slope steep enough that the cut sounds like a sharp band edge rather than a gentle roll-off. The measured result is that content an octave above the corner sits about eighteen decibels down, which is what makes the band sound closed rather than merely dark. The drive stage at the end applies a smooth saturation, which adds harmonics of the material that survived the filtering and mimics the way an overdriven transmitter or a small speaker behaves. The two patches differ mostly in bandwidth: the AM setting is narrow enough to sound obviously like an old receiver, while the FM setting keeps more than three times the upper bandwidth, so it reads as a clean broadcast rather than a crackling one. The make-up gains compensate for the energy the filtering removed, so both patches come out at a similar level to the input.

Where it is limited:

No static, crackle or interference is added.
No mono collapse, which a real AM receiver would impose.
The two voicings have fixed corners, with only the tone tilt adjustable.
No carrier noise or tuning artefacts.
Nothing about the sound before the filtering is preserved.
Output is sixteen bit WAV.

Use it to place a voice inside a radio broadcast, to give a part a lo-fi mid-forward colour, or to make a mix sound as though it is coming through a small speaker. When the target is the narrower band of a telephone line rather than a broadcast receiver, the telephone effect covers three to three and a half kilohertz, and when the aim is to degrade resolution rather than bandwidth, the bitcrusher produces that kind of artefact instead.

How to use Radio Effect

Drop an audio file onto the panel.
Choose the AM voicing for an old receiver or the FM one for a cleaner broadcast.
Adjust the tone tilt if the midrange wants to be brighter or warmer.
Process the file and download the radio voiced WAV.

When to use Radio Effect vs related tools

Radio Effect is the tool for the voice of a broadcast receiver, which is narrower and more saturated than most other lo-fi treatments. Telephone Effect applies the narrower band of a phone line instead, and Old Tape Effect imitates a recording medium rather than a transmission. When the target is resolution rather than bandwidth, Bitcrusher Effect degrades the level quantisation instead.

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