TheCodeBreakers
possible in a very crude form by means of mechanical phonographs.
From a practical point of view, however, nonelectrical scramblers may be
ruled out. None ever seems to have been constructed.
tJtlNSUKS, S^KAJVLBLtKB, AIN1J
shifted to 1,500. One of 2,800 c.p.s. would then be enciphered to 800.
Band-splitting splits the frequency band into several smaller bands
and interchanges these. Filters can divide a 250-to-3,000 band into five
subbands of 550 cycles each: subband A of 250 to 800, subband B of 800
to 1,350, subband c of 1,350 to 1,900, subband D of 1,900 to 2,450, and
subband E of 2,450 to 3,000. Then the scrambler's switches and circuits
may replace A by c, B by D, c by E, D by A, and E by B, thus jumbling the
normal tones. The better band-splitters shift these substitutions every
few seconds or milliseconds. The result sounds something like a
recording of a Mah-Jongg game played too fast.
Masking systems bury the voice signal in noise. The music from a
annaabi.ee 
