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Low delay LPC and MDCT-based audio coding in the EVS codec

: Fuchs, G.; Helmrich, C.R.; Markovic, G.; Neusinger, M.; Ravelli, E.; Moriya, T.


Institute of Electrical and Electronics Engineers -IEEE-; IEEE Signal Processing Society:
IEEE 40th IEEE International Conference on Acoustics, Speech and Signal Processing, ICASSP 2015. Proceedings. Vol.8 : 19-24 April 2015, Brisbane, Australia
Piscataway, NJ: IEEE, 2015
ISBN: 978-1-4673-6997-8
ISBN: 978-1-4673-6998-5
International Conference on Acoustics, Speech, and Signal Processing (ICASSP) <40, 2015, Brisbane>
Fraunhofer IIS ()

Speech coders operating in time domain can be extended with a frequency domain mode to improve encoding of music, even though this is challenging at low delay. In such a scenario, the short analysis window limits the benefit of the transform coder, while a delayless switch between the two coders constrains the system further. The paper presents an LPC and MDCT-based audio coder part of the new 3GPP codec for Enhanced Voice Services, which aims to solve the issues. Several advanced coding tools are introduced to alleviate the constraints: transient handling is improved, harmonic structures are better preserved, and the modeling of the zero-quantized frequencies is enhanced. Test results show that the obtained low-delay switched coder brings a clear improvement over a speech coder and is competitive even in comparison to audio coders with higher delay.