Speech Bandwidth Extension Using Data Hiding Based on Discrete Hartley Transform Domain

Abstract

The public switching telephone network restricts speech signals to a narrow bandwidth (NB) of 0.3-3.4 kHz, which results in a perceived reduction in quality due to the missing upper bandwidth (UB) spectrum of 3.4-7 kHz. This paper proposes a speech bandwidth extension method that reconstructs the missing UB spectrum using side information. A sender side obtains a UB spectral envelope and relative gains between NB and UB excitation signals as side information. Side information is then converted into a binary signal using two codebooks. Using speech steganography based on the discrete Hartley transform (DHT) domain, the proposed method robustly embeds the binary signal into an amplitude spectrum of the NB speech signal in the high-frequency bandwidth of 3.4-4.6 kHz to produce a composite narrow bandwidth (CNB) speech signal. On a receiver side, the missing UB spectrum is reconstructed using side information extracted from the CNB speech signal. Theoretical and simulation analysis shows that side information is retrieved from the CNB speech signal accurately. Subjective listening tests and objective measures also show that the proposed method enhances the quality of the NB speech signal by reconstructing the missing UB spectrum.

Complex-Domain Pitch Estimation Algorithm for Narrowband Speech Signals

“…The proposed method thus introduces phase differences between harmonics as an additional cue for pitch estimation. Our previous study showed that the phase difference between harmonics could be derived using the pitch [34]. When the phase spectrum for the higher-order harmonic is shifted by the theoretical value, it agrees with the phase spectrum for the lowest-order harmonic.…”

“…However, the phase spectrum is unstable due to noise, so the phase difference between the lowest-order harmonic and other harmonics is further calculated. By using (9), the phase difference between harmonics is defined as follows:…”

“…Artificial bandwidth extension (ABE) is a speech enhancement approach for narrowband speech signals, which reconstructs the missing lower spectrum (0-300 Hz) and upper spectrum (3400-7000 Hz) using the existing narrowband spectrum of 300-3400 Hz [6], [7], [8], [9], [10], [11], [12]. Because of the missing lower-order harmonics, the narrowband speech signal has a partial harmonic structure.…”

“…Researchers have worked on pitch estimation for a long time [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34]. Because speech signals have pseudo-periodicity with a short frame length, time-domain pitch estimation algorithms estimate a pitch using an autocorrelation function [13], [14], [15], [16].…”

“…Note that harmonics are the key to pitch estimation, as known in frequency-domain pitch estimation algorithms. Our previous study [34] utilized the phase difference between harmonics, which is defined as the two-step phase difference between successive analysis frames and between the lowest-order harmonic and other harmonics. While group delay, which is useful for speech signal processing, differentiates the phase spectrum for frequency, the phase difference between harmonics focuses only on harmonics and is theoretically derived using the pitch.…”