Why PSK31 encodes text with Varicode, a variable-length alphabet in which the most frequently used characters (space, e, t) get the shortest bit patterns and rare characters get longer ones. That keeps the average throughput near 31.25 baud typing speed while holding the signal in about 31 Hz of bandwidth. The idea is the same efficiency trick Morse code uses: common letters, short symbols.
Watch out RTTY is the usual trap, but it uses Baudot, a fixed 5-bit code for every character, so all characters take the same time to send.
PSK31 = Varicode = VARiable. Baudot (RTTY) is always 5 bits, no more, no less.
Varicode varies: PSK31 gives 'e' a short code and 'z' a long one, like Morse. Baudot (RTTY) is always 5 bits. Pool tell: 'RTTY' is never the answer anywhere in this pool.