From HwB

Sound chip from Texas Instruments.

As per datasheet: "The SN76477 complex sound generator is a monolithic chip combining both anolog (bipolar) and digital (I2L) circuitry. It includes a noise generator, a voltage-controlled oscillator (VCO), and a super-low-frequency oscillator (SLF) together with a noise filter, mixer, attack/decay circuitry, audio amplifier, and control circuitry to provide noise, tone, or low-frequency sounds and any combination of these."