Robert Lawlor

High quality time-scale modification of speech using a peak alignment overlap-add algorithm (PAOLA)

The duration of a speech passage can be altered using audio time-scale modification techniques. Time-scale modification can be achieved in the time domain by segmenting the input signal into overlapping frames and recombining the frames with an overlap differing from the analysis overlap. We present a time-scale modification algorithm that uses a simple peak alignment technique to synchronize overlapping synthesis frames. The peak alignment overlap-add (PAOLA) algorithm also takes advantage of waveform properties to ensure a high quality output for the minimum number of iterations. The new algorithm produces a time-scaled output of approximately equal quality to that of an adaptive implementation of the commercially popular synchronised overlap-add (SOLA) algorithm, but offers a computational saving ranging from a factor of 15 (for a time-scale factor of 0.5) to 170 (for a time-scale factor of 1.1).

Time-scale modification of music using a synchronized subband/time-domain approach

Time-domain audio time-scaling algorithms are efficient in comparison to their frequency-domain counterparts, but they rely upon the existence of a quasi-periodic signal to produce a high quality output. This requirement makes them unsuitable for direct application to complex multi-pitched signals such as polyphonic music. However, it has been shown that applying time-domain algorithms on a subband basis can resolve this issue. Existing subband/time-domain approaches result in a reverberant/phasy artifact being introduced into the output due to poor synchronization between time-scaled subbands. This paper presents a number of synchronization schemes that greatly reduce the amount of reverberation/phasiness introduced into the time-scaled output by existing subband/time-domain approaches.

Audio time-scale modification using a hybrid time-frequency domain approach

Frequency-domain approaches to audio time-scale modification introduce a reverberant artifact into the time-scaled output due to a loss in phase coherence between subband components. Whilst techniques have been developed which reduce the presence of this artifact, it remains a source of difficulty. A method of time-scaling is presented that reduces the presence of reverberation by taking advantage of some flexibility that exists in the choice of phase required so as to maintain horizontal phase coherence along frequency-domain subband components. The approach makes use of appealing aspects of existing time-domain and frequency-domain time-scaling techniques.

Time-scale modification of music using a subband approach based on the bark scale

Time-domain time-scaling algorithms are efficient in comparison to their frequency-domain counterparts, but they rely upon the existence of a quasi-periodic signal to produce a high quality output. This requirement makes them unsuitable for use on multi-pitched signals such as polyphonic music. However, time-domain techniques applied on a subband basis can resolve the multi-pitch problem. We propose an improved subband implementation based upon the bark scale for the time-scale modification of music. The new subband approach is supported by psychoacoustic and music theory and subjectively through informal listening tests.