Problem 60743. Bit Stream conversion to Audio Frequency Shift Key using Bell 202 (Modem)

There must be something I'm missing here, and I can't make sense of the plot you posted. Shouldn't the final value be sin((1200 + 2200 + 1200) / (1.2e5/600) = -0.846220404175171, rather than roughly -0.7?

For the case in the plot, binaryToBell202('101',1.2e5,600), there are three sine waves for the three bits, each of which is 1/600 seconds long. The first sine wave, at 1200Hz, goes through exactly two periods, so it starts and ends at zero; the second, at 2200Hz, goes through 3+(2/3) periods, so it starts at zero and ends at sin(2*pi*(2/3))=-sqrt(3)/2=-0.866; the third sine wave goes through exactly two periods again, and therefore should end at -0.866 again. This is independent of the sample rate. If you are trying to match the sine waves at the discrete points defined by the sample rate, then it gets more confusing.

I should have prefaced the previous comment with "If I understand what is going on, ".