@InProceedings{Das2020_445,
<br/>   author = {Sneha Das and Tom Bäckström},
<br/>   booktitle = {Studientexte zur Sprachkommunikation: Elektronische Sprachsignalverarbeitung 2020},
<br/>   title = {Low-Complexity Postfilter using MDCT-Domain for Speech and Audio Coding},
<br/>   year = {2020},
<br/>   editor = {Andreas Wendemuth and Ronald Böck and Ingo Siegert},
<br/>   month = mar,
<br/>   pages = {109--116},
<br/>   publisher = {TUDpress, Dresden},
<br/>   abstract  = {Postfilters are used in speech and audio codecs to improve the quality of
the decoded signal. Recent studies have shown that postfilters using speech models
can considerably improve the output quality of the signal. In our previous work,
we proposed a postfilter for frequency-domain speech coding which took advantages
of the time-frequency correlation inherent to the speech magnitude spectrum.
However, while the proposed approach showed substantial improvement in the output
speech quality, it operates in the STFT-domain, whereas state-of-art transform
domain coding is implemented in the modified discrete cosine transform (MDCT)
domain. As a result, the decoded signal has to be first transformed back to the
time-domain and then to the frequency-domain before the postfilter can be applied,
thus increasing the algorithmic delay and complexity. In this work, we adapt the
context-based postfiltering method to the MDCT-domain, such that the postfilter
can be directly applied on the decoded signal within the codec framework. However,
we observe that the gains obtained from postfiltering in the MDCT-domain
is half of that in the STFT-domain. Further analysis indicates that the correlation
between coefficients in the MDCT-domain is lower than the correlations in
the STFT-domain. Hence, the modelling methods employed in the STFT-domain
postfilter are not directly applicable to a postfilter using the MDCT. To improve performance,
we propose to jointly model a pair of MDCT coefficients as a complexvalued
pseudo spectrum. The proposed approach shows an average perceptual-
SNR (PSNR) improvement of 1.5 dB over a plain MDCT approach, which is similar
to the quality with a STFT-domain postfilter.},
<br/>   isbn = {978-3-959081-93-1},
<br/>   issn = {0940-6832},
<br/>   keywords = {Acoustic Signals},
<br/>   url = {https://www.essv.de/pdf/2020_109_116.pdf},
<br/>}