Hybrid noise shaping for audio coding using perfectly overlapped window

TL;DR

This paper introduces a novel audio coding framework combining modulated complex lapped transform, transform coded excitation, and complex LPC-based temporal noise shaping, achieving improved efficiency and quality at low bit rates.

Contribution

It presents a new hybrid noise shaping method with a 50% overlap window and adaptive bit allocation, enhancing low bit-rate audio coding performance.

Findings

Superior objective metric performance

Enhanced subjective listening quality

Effective noise shaping with low bit-rate efficiency

Abstract

In recent years, audio coding technology has been standardized based on several frameworks that incorporate linear predictive coding (LPC). However, coding the transient signal using frequency-domain LP residual signals remains a challenge. To address this, temporal noise shaping (TNS) can be adapted, although it cannot be effectively operated since the estimated temporal envelope in the modified discrete cosine transform (MDCT) domain is accompanied by the time-domain aliasing (TDA) terms. In this study, we propose the modulated complex lapped transform-based coding framework integrated with transform coded excitation (TCX) and complex LPC-based TNS (CTNS). Our approach uses a 50\% overlap window and switching scheme for the CTNS to improve the coding efficiency. Additionally, an adaptive calculation of the target bits for the sub-bands using the frequency envelope information based on the quantized LPC coefficients is proposed. To minimize the quantization mismatch between both modes, an integrated quantization for real and complex values and a TDA augmentation method that compensates for the artificially generated TDA components during switching operations are proposed. The proposed coding framework shows a superior performance in both objective metrics and subjective listening tests, thereby demonstrating its low bit-rate audio coding.