P. Dutilleux, G. De Poli and U. Zölzer
In this chapter we discuss several time domain algorithms which are a combination of smaller processing blocks like amplitude/phase modulators, filters and delay lines. These effects mainly influence the pitch and the time duration of the audio signal. We will discuss two approaches for time stretching of audio signals. They are based on an analysis stage, where the input signal is divided into segments (blocks) of fixed or variable length, and a synthesis stage where the blocks of the analysis stage are recombined by an overlap and add procedure. These time stretching techniques perform time scaling without modifying the pitch of the signal. The further section focuses on pitch shifting, and introduces three techniques: block processing based on time stretching and resampling, delay line modulation and pitch-synchronous block processing. The last section on time shuffling and granulation presents a more creative use of time-segment processing. Short segments of the input signal are freely assembled and time placed in the output signal. The wide choice of strategies for segment organization implies a sound composition attitude from the user.
Keywords: Time Stretching, Time Scaling, Pitch Shifting, Frequency Scaling, SOLA, PSOLA, Shuffling, Granulation