STA321 is a 4-channel digital audio system produced by ST company. It has a high efficiency FFX™ class-D modulator, 100-dB dynamic range, two stereo channels, 16-bit stereo ADC input, PGA and microphone biasing, analog and digital multiplexing/mixing capability, 4-channel input sample rate converter (8 kHz to 192 kHz), four channels of 24-bit audio processing, flexible channel mapping and routing, output configurations: 2.0-2.1-4.0-Mono, embedded CMOS bridge, pfStart™, simultaneous playback and recording, pre and post mix stages, individual channel and master gain/attenuation, digital gain/attenuation -105 dB to +36 dB in 0.5 dB steps, soft volume update and muting, DC blocking selectable high-pass filter, selectable de-emphasis filter, up to 13 28-bit user programmable biquads (EQ) per channel, bass/treble tone control, ternary, binary or phase shift modulation, PWM output, headphone output with jack detector, I2C control.