Perceptual relevance of the temporal envelope to the speech signal in the 4–7kHz band

Abstract

The perceptual relevance of adopting the temporal envelope to model the frequency band of 4–7kHz (highband) in wideband speech signal is described in this letter. Based on theoretical work in psychoacoustics, we find out that the temporal envelope can indeed be a perceptual cue for the high-band signal, i.e., a noiseless sound can be obtained if the temporal envelope is roughly preserved. Subjective listening tests verify that transparent quality can be obtained if the model is used for the 4.5–7kHz band. The proposed model has the benefits of offering flexible scalability and reducing the cost for quantization in coding applications.

Speech Bandwidth Extension Using Temporal Envelope Modeling

“…As shown in [5], highband temporal envelopes require just the half of the bandwidth of subband signals to have perceptually meaningful bandwidth. To constrain filtering effect of the input signal to be band-limited, a decimation process is required.…”

“…In SBE, it is desirable to ignore perceptually unimportant components, but to concentrate on perceptually important information. In addition, since temporal envelopes have bandlimited characteristics [5], they can be compressed by comparing the bandwidths of corresponding subband signals, which enables an efficient prediction in view of signal processing.…”

“…Here, we call the 3-4 kHz band the intermediate band since this band plays the role of a bridge from the narrowband to the highband. The temporal envelope of the intermediate band, , is first calculated with a temporal envelope extraction method using the Hilbert transformation [5]. By filtering the temporal envelope of the intermediate band with the estimated transformation filters, , and scaling them with the estimated energy ratios, , we can obtain the temporal envelopes of the subband signals, .…”

“…The model is motivated by temporal masking effects, where temporal masking thresholds look similar to temporal envelopes of corresponding band signals if they are in the high-frequency band [4], [7]. In addition, just-noticeable amplitude variation (JNAV) and just-noticeable frequency variation (JNFV) psychoacoustically guarantee the suitableness of the TEM [5].…”

“…In our previous work [5], we showed that the temporal envelope of the highband signal could be an important perceptual cue of the highband components and rapidly varying components (fine structure) in the temporal domain are not as important. In other words, a perceptually identical sound can be synthesized if we only model the temporal envelope of the highband signal correctly.…”