Enhancing Frequency Shifted Speech Signals in Single Side-Band Communication

The spectral quality of speech signals communicated over high-frequency single side band (HF-SSB) radio channels is affected by acoustic artifacts like linear frequency transpositions. In this letter, we propose an approach to automatically estimate and correct for the frequency shift given the degraded signal at the SSB receiver. The proposed method utilizes the harmonic nature of the speech signal in the voiced regions. The fundamental harmonic frequency, obtained from an autoregressive model of the spectrum, is used to estimate the offset value for the current frame. The offset values from the adjacent frames are pooled together to provide the most likely estimate for the received signal. Various experiments are performed on frequency shifted degraded speech signals received from the HF-SSB channel. The enhanced speech signal is also applied for a language identification task (LID) where the models are trained on speech data without any frequency shift. In these experiments, the proposed algorithm provides significant improvements over other baseline offset estimation methods in terms of accuracy of offset estimation as well as the LID system performance (with relative improvements of about 10-25%).