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BA1701

VSC∗ system processor IC

ROHM Semiconductor 

Audio ICs

FCircuit operation

(1) System construction

The BA1701 is a monolithic audio-compression system

controller IC that uses VSC.When used in combination

with an analog delay circuit, low-pass filter, and tape

speed controller, it can replay recorded audio at 1 to 2.5

times the recording speed, without altering the pitch (see

BA1701

Fig. 3).

The BA1701 has a built-in motor driver control circuit that

is synchronized with the pitch control that allows the sys-

tem to be built with just one pitch control potentiometer

(see Fig. 4).

(2) Principles of audio compression (see Fig. 5)

When recorded audio (A) is replayed at high speed, the

pitch of the audio increases in proportion to the playback

speed (B). By expanding this using an analog delay cir-

cuit, a compressed audio signal with the same pitch as

the original recorded signal is obtained (C). Partial audio

dropout occurs when the audio is expanded, but due to

the diffuse nature of speech, the expanded audio does

not sound unnatural to the human ear.

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