This chapter deals with audio processing and contains theoretical discussions and MATLAB coding examples, including Basic MATLAB functions, Audio System Toolbox (AST) functions, DSP System Toolbox (DSPST) functions, and Signal Processing Toolbox (SPT) functions related to the following topics: waveform, phase, sampling frequency, aliasing, sinusoidal tones, composite notes, Fourier domain representation of audio signals, coefficients and basis functions, reading and writing digital audio files, plotting audio waveforms, recording and playback of digital audio, oscilloscope display, wavetable synthesizer, reverberation, noise gate, dynamic range compressor and expander, crossover filter, pitch, voice activity detection, momentary short-term and integrated loudness, mel frequency cepstral coefficients, time scope, sine wave generator, spectrum analyzer, array plots, playback of Musical Instrument Digital Interface notes, using a variety of instrument sounds, finite impulse response (FIR), infinite impulse response (IIR), window functions, frequency representations, spectrogram, signals with variable frequencies, low-pass and high-pass FIR filters, low-pass and high-pass IIR filters, band-stop and band-pass FIR filters, band-stop and band-pass IIR filters, and development of Simulink models for audio processing tasks.