Kleijn, W. Bastiaan (School of Engineering and Computer Science, Victoria University of Wellington, New Zealand)
Skoglund, Jan (Google, Inc., 1600 Amphitheatre Parkway, Mountain View, USA)
We present methods that are relevant for the commonly used pitch predictors in speech/audio coders. We first discuss optimal pre- and post-filtering and derive a general result that post-filtering is more effective than pre-filtering. This, together with the perceived nature of the distortion, suggests the omission of the pre-filter if system delay is critical. We propose a practical paired-zero filter design for the low-rate regime. We extend this design to handle frequencydependent periodicity levels. We also provide a general performance measure for a post-filter that only uses information available at the decoder. This criterion allows the optimization or selection of a postfilter without increasing the rate. Our experiments show that the resulting methods provide state-of-the-art performance both for objective measures and in terms of quality as perceived by test subjects.