Three controls shape the voice that reaches the antenna on SSB: mic gain, the optional speech processor (compression), and ALC, the automatic level control that watches the result. The goal is a clean, readable signal at the power the radio is rated for, without a wide, splattery one.
Set the levels in order: mic gain first (watch ALC), then add compression only if you need it.
Mic gain and ALC
The final amplifier can only be driven so hard. ALC is a feedback circuit that detects too much drive and turns it down, and the ALC meter shows you when it is acting. Past that point, more gain just flattens the tops of the speech peaks.
Set mic gain so the ALC just touches its zone on voice peaks. More is not louder, only dirtier.
Flattened peaks mean distortion and extra frequencies on either side of your signal (intermodulation products), so your signal gets wider and neighbours hear it as splatter. More mic gain does not give more power once ALC is working; it only gives more distortion.
To set mic gain:
Turn the speech processor off and use the mic at its normal distance.
Speak at your normal conversational level, and watch the ALC meter.
Raise the gain until the meter just touches the radio's ALC zone on your loudest peaks, and no further.
Ask for a report, or listen to a recording of your own signal.
Compression
Speech is bursty: the peaks are far higher than the average. A speech processor compresses the audio so quiet syllables are lifted toward the loud ones. The peaks stay at the transmitter's limit, so the average power rises while the peak does not. The signal sounds louder and "punches through" a crowded band.
Peak power is capped by the transmitter. Processing raises the quiet parts, so the average goes up.
Average power×2.4
Peak powersame
Level of processing
Result
Off or light (a few dB)
natural voice, a modest gain in readability
Heavy
harsh, tiring voice, more distortion, more noise brought up with the speech
Compression is most useful for weak-signal or DX work and on noisy bands. In a quiet band with a strong signal, or in conversation with a friend, less is more. Some radios compress the audio; others clip the RF waveform and filter it afterward, which can add more talk power but also distorts sooner when overdone.
Clean audio first
Processing cannot fix poor audio. Before reaching for it:
Keep the mic at a consistent distance, a few finger-widths from your mouth, and speak across rather than into it to reduce pops.
Check for RF feedback: if the power meter or ALC jumps when you touch the cable, RF is getting into the mic line. A common-mode choke on the cable usually helps.
Use the radio's transmit equalizer or bandwidth setting to trim extra bass, which wastes power below the voice range. See Microphones and headsets.