The 1930s vocoder pioneered reducing speech to slowly-varying parameters to cut bandwidth

Evidence

Speech coding methods thus use the principle behind the vocoder (short for voice encoder), which was developed in the 1930s (Dudley, 1940). In the original implementation, the input speech signal was passed through a filter bank, and the signal in each band was passed through an envelope follower. The control signals from the envelope followers was communicated to the decoder. The decoder applied these (amplitude) control signals to corresponding filters in the synthesizer. Since the control signals changed only slowly compared to the original speech waveform, the bandwidth required to transmit speech was reduced, and the parameters could be modelled statistically. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 2225

Categorization

• DEFINE: Explains how the vocoder works mechanically and why it saved bandwidth, defining the term historically.
• corroborated: 2 independent passages support this claim — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 2225
• XREF: connects to: Bell Labs 1930s tests found three channels sufficed to transmit a soundstage; Noise-vocoding degrades speech by replacing detail with band-limited noise envelopes.; Audio compression exploits masking to discard inaudible signal parts — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 2020 (+2 more)

Broader Connections

• Noise-vocoding degrades speech by replacing detail with band-limited noise envelopes. #expands (0.80)
• Very low bit-rate audio coding requires working in the frequency domain #expands (0.80)
• Audio compression exploits masking to discard inaudible signal parts #expands (0.75) — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 2020
• Perceptual coders exploit masking to cut audio storage and bandwidth #expands (0.75) — David Howard, Jamie Angus, coustics and Psychoacoustics, 1656