The eye reads a number; the ear reads a change.
To read a needle you must look at it, and looking costs a movement of the eyes, a moment of focus and a moment of interpretation — call it a second, in a cockpit where a second is twenty degrees of heading. Hearing costs nothing. The ear resolves a pitch change of well under one per cent, it does it continuously, and it does it while you are looking somewhere else entirely. That is the whole argument for audio, and it is why a vario without a speaker is half an instrument.
It also explains a quirk of good thermalling technique: the pilots who centre fastest are not reading the strongest lift, they are reacting to the moment the pitch starts to rise. A rising tone in the first quarter of a turn is information about where the core is, and it arrives long before any number is worth reading.
Pitch is the climb; the chirp confirms it.
The mapping from vertical speed to frequency is exponential, because hearing is. A fixed number of hertz per metre per second sounds compressed at the top and coarse at the bottom, whereas a fixed number of octaves per metre per second sounds even across the whole range. A common arrangement puts zero at around 500 Hz and roughly doubles the frequency every two metres a second of climb.
Pitch alone is ambiguous, though — a slowly drifting tone is easy to mishear. So climb is also interrupted, and the interruption rate rises with the climb: a slow blip in weak lift, a rapid chatter in a strong core. Sink is left continuous and low, which is unmistakable and, importantly, unpleasant. Two channels carrying the same number mean you can identify a climb without having consciously listened to it.
Listen to the mapping.
Press Listen, then sweep the climb slider slowly from −3 to +3 and notice where you stop needing to look at the screen. Widen the dead band and the weak edges of the thermal go quiet — comfortable on a rough day, and a good way to fly past the top of a dying climb without noticing. Switch to CRUISE and the same speaker answers a different question entirely.
The silence band is a design decision, not a fault.
A variometer with no dead band chatters continuously, because the air is never exactly still and neither is your flying. So every instrument has a band around zero in which it says nothing — Vario silence in an LX menu, dead band everywhere else — and choosing its width is a real trade. Too narrow and the cockpit is exhausting, and you stop hearing the instrument in the way you stop hearing a fan. Too wide and the weak lift at the top of a climb is inaudible — you fly out of a dying thermal in silence and never learn where it ended.
There is a second band worth knowing about. In speed-command mode there is a second band — <b>SC silence</b> in an LX menu — in which the tone stays off while your speed is close enough to the recommended one, so it only speaks when your speed is genuinely worth correcting. Without it, speed command would be a permanent nag.
In the cruise the speaker changes the subject.
Switch to speed command and the audio stops describing the air and starts describing you. The number driving it is no longer the vario reading but the difference between your speed and the speed the MacCready setting recommends, and the tone is an instruction: one sound means accelerate, the other means slow down, silence means you are close enough. Which sound means which varies between manufacturers — check yours.
The input matters as much as the mapping. Speed command driven by the raw vario would react to your own pull-ups and pushovers, so it is driven by netto — the vertical motion of the airmass with your own sink removed — or by relative, which subtracts the sink you would have while circling. Which of those your instrument uses is a setting worth finding once and then leaving alone.
En tu cabina.
Two settings deserve five minutes on the ground before the season. The dead band, because it decides how much of the weak air you get told about. And the response or filter setting, which decides how old the news is by the time you hear it — the vario response article is entirely about that trade. If your tone reacts to every stick movement rather than to the air, the compensation is the place to look: total energy explains why. Then fly one thermal with a sheet of paper over the instrument and find out how much of your centring was ever visual.
Zero, positive and negative tone frequencies, a silence band and an audio test that sweeps them so you can set them by ear.
Separate vario and speed-command voices, each with its own silence, on one indicator.
The compensated air data the tone is made of, before any of it reaches a speaker.