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Finally, Figures 10.22 and 10.23 show the time and frequency domain plots for the SOLA-FS algorithm (a time-domain method). SOLA-type algorithms perform slow-down by repeating frames locally. (In this case, each frame could be repeated once to accomplish the $ 2\times $ slow-down.) They maximize cross-correlation at the ``loop-back'' points in order to minimize discontinuity distortion, but such distortion is always there, though typically attenuated by a cross-fade on the loop-back. We can see twice as many ``carrier cycles'' under each beat, meaning that the beat frequency (amplitude envelope) was not preserved, but neither was it severely distorted in this case. SOLA algorithms tend to work well on speech, but can ``stutter'' when attack transients happen to be repeated. SOLA algorithms should be adjusted to avoid repeating a transient frame; similarly, they should avoid discarding a transient frame when speeding up.

Figure 10.22: SOLA-FS waveforms at 2X expansion.

Figure 10.23: SOLA-FS spectra at 2X expansion.

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``Spectral Audio Signal Processing'', by Julius O. Smith III, W3K Publishing, 2011, ISBN 978-0-9745607-3-1.
Copyright © 2022-02-28 by Julius O. Smith III
Center for Computer Research in Music and Acoustics (CCRMA),   Stanford University