14.4k modem sound (V.32bis)
The 14 400 bit/s modem of the early 1990s: answer tone, a two-tone warble that measures the line, then training hiss and rate signals.
Heads up: modems are loud. Playback starts at −12 dB and runs through a limiter.
AT console (Hayes commands)
Event list (the spectrogram as text)
How a V.32 bis call starts
V.32 bis (1991) predates V.8, so there are no menus. The answerer sends the plain V.25 answer tone, 2100 Hz with phase reversals every 450 ms. After hearing it for at least 1 s, the caller starts sending carrier state A over and over, which on an 1800 Hz carrier is a pure 1800 Hz tone (AA).
The answerer replies with AC: states A and C alternating at 2400 symbols per second. Because A and C are opposite points, the result is two tones at 1800 ± 1200 Hz, 600 and 3000 Hz. That is the warble. Each side then flips phase (CA, CC) exactly 64 symbols after hearing the other's flip, and both measure the round trip (§6).
Training and rates
Then each modem sends S, S̄ and TRN, scrambled ones mapped onto four states (the hiss), followed by the 16-bit rate signals R1, R2 and R3 (Table 5/V.32 bis), which agree on 4800, 7200, 9600, 12 000 or 14 400 bit/s. A single E sequence names the final rate. The scramblers here reproduce, bit for bit, the patterns printed in §5.2.3.
Approximate: the 14 400 bit/s data uses points of the 128-point cross without the trellis code.