Channel capacity is b * log2 (1 + snr) where b is the bandwidth in Hz and snr is the linear signal-to-noise ratio. The voice passband in the old telephone syst

Channel capacity is b * log2 (1 + snr) where b is the bandwidth in Hz and snr is the linear signal-to-noise ratio. The voice passband in the old telephone system is 3 kHz. And 60 dB SNR average over the passband was typical for a clear voice channel: 3000 * log2 1000000 = 59,800 bits per second.