We propose an audio codec that addresses the low-delay requirements of some applications such as network music performance. The codec is based on the modified discrete cosine transform (MDCT) with very short frames and uses gain-shape quantization to preserve the spectral envelope. The short frame sizes required for low delay typically hinder the performance of transform codecs. However, at 96 kbit s and with only 4 ms algorithmic delay, the proposed codec out-performs the ULD codec operating at the same rate. The total complexity of the codec is small, at only 17 WMOPS for real-time operation at 48 kHz.
@cite_4: Low latency audio coding gains increasing importance among upcoming high quality communication applications like video conferencing and VoIP. This paper provides a comparison of two low latency audio codecs suitable for these tasks: MPEG-4 ER AAC-LD and ITU-T G.722.1 Annex C. Despite their similar coding strategies, both codecs show significant differences with respect to used tools and coding performance. A comparison of the coding tools is provided and the influence on different signal classes is discussed.
AAC-LD @cite_4 is another low-delay audio codec whose total algorithmic delay can range from 20 ms to around 50 ms, depending on the sampling rate and bit reservoir size. However, its complexity is higher than that of the proposed codec.