Building a clean frequency plan is one thing; understanding what happens between the mic and the receiver is another. Plenty of engineers can scan a spectrum and lay out carriers, yet stumble on the three mechanisms that really make a link reliable: companding, diversity reception and squelch. Master them and you know why a system drops out, hisses or mutes, and how to fix it without guesswork.
Start with the chain. A transmitter, housed in a bodypack or in the handle of a handheld mic, turns audio into a radio signal and sends it on a carrier. At the other end, a receiver picks up that carrier, extracts the audio and hands it to the console. In between, radio imposes its constraints, and that is where the three mechanisms come in.
Companding, the secret of silence
Analog FM radio has an enemy: the noise floor. Sending a voice straight onto a carrier would leave a constant hiss, worst of all in quiet passages. Manufacturers therefore adopted companding, a word built from “compression” and “expansion.” At the transmitter, the signal’s dynamics are compressed, narrowing the gap between soft and loud sounds. At the receiver, an expander applies the reverse and restores the original dynamics.
The trick lies in its effect on noise. Because the soft signal was lifted before the radio trip, then pushed back down on arrival, the hiss the link adds is pushed down with it. The result is a link that sounds far quieter than radio alone would allow. This process also explains some audible faults when a system is poorly set, such as a “pumping” feel on close vocals or a particular colour on transients. Recent digital systems skip companding, since they transmit a coded stream, but they inherit other constraints: latency to watch and an all-or-nothing behaviour at the edge of range.
Diversity reception, so you stop dropping out
A radio wave never travels in a straight line on a stage. It bounces off structures, the audience, the lights, and these multiple paths recombine at the antenna. At times two paths almost cancel, and the signal collapses at one precise spot, for the length of a performer’s step. That is the classic multipath dropout, a reception hole that has nothing to do with distance.
The answer is diversity. A true diversity receiver carries two antennas and two complete receiver front-ends. At every moment it compares the two signals and keeps the better one, or combines them. When one antenna falls into a null, the other stands a strong chance of being clear, because the two do not see exactly the same field. The difference from a single-antenna receiver is dramatic on a crowded stage. Mind the marketing vocabulary: some units advertise “diversity” with two antennas but a single receiver switching between them, which is less robust than a true dual chain. To get the most from those antennas, antenna distribution lets you move them toward the stage and share several receivers.
Squelch, the anti-noise gate
The last mechanism is squelch. When the radio signal gets too weak, for instance if the performer walks out of range or the transmitter switches off, the receiver may spit out a violent burst of noise, analog or digital, very unpleasant in the house. Squelch is the gate that cuts the audio output as soon as the signal drops below a threshold. Modern systems do not just measure received power, they look for a pilot tone or a digital key specific to the transmitter, so they do not mistake interference for the real signal.
Setting it takes a light touch. Too high a squelch cuts the link too early and causes dropouts while the signal is still usable. Too low a squelch lets noise bursts through at the edge of range. The right move is to set the threshold just above the ambient noise measured with no transmitter on, then check it by walking the performer to the limits of the playing area.
Analog or digital, the logic stays the same
Digital links reshuffled the deck but did not flip the table. They replace companding with signal coding, which removes hiss by design and opens the door to encryption. In return, they add a latency you must account for in a monitor system, and their dropout is more abrupt, without analog’s grey zone of gradual degradation. Diversity, for its part, stays essential in both worlds, because wave physics does not change. Squelch exists in digital too, often as a decode-quality threshold.
In practice, these three ideas hang together. A careful frequency plan avoids interference, diversity absorbs coverage holes, companding or the codec handles silence, and squelch protects the house at the edge of range. To build that plan upstream, our guide to planning RF frequencies covers scanning and intermodulation. And when it comes to gear, compatible capsules like the Sontronics SOLO W2 or the sE Electronics V8 are a reminder that the transmitter is only one link, and the capsule matters as much as the radio.
My take
The wireless mic is one of those tools judged on how little you notice it, and noticed only the day it fails. Understanding the companding, diversity and squelch trio turns you from a user into an engineer who can diagnose. The good news is that these principles predate digital and still hold today. A true diversity receiver, two well-placed antennas and a squelch set by ear are enough to sleep easy the night before a live show.
