Perceptual coding of digital audio

Abstract

I. INTRODUCTIONAudio coding or audio compression algorithms are used to obtain compact digital representations of high-fidelity (wideband) audio signals for the purpose of efficient transmission or storage. The central objective in audio coding is to represent the signal with a minimum number of bits while achieving transparent signal reproduction, i.e., generating output audio that cannot be distinguished from the original input, even by a sensitive listener ("golden ears"). This paper gives a review of algorithms for transparent coding of high-fidelity audio.The introduction of the compact disk (CD) in the early eighties [1] brought to the fore all of the advantages of digital audio representation, including unprecedented high-fidelity, dynamic range, and robustness. These advantages, however, came at the expense of high data rates. Conventional CD and digital audio tape (DAT) systems are typically sampled at either 44.1 or 48 kilohertz (kHz) using pulse code modulation (PCM) with a sixteen bit sample resolution. This results in uncompressed data rates of 705.6/768 kilobits per second (kbps) for a monaural channel, or 1.41/1.54 megabits per second (Mbps) for a stereo pair at 44.1/48 kHz, respectively. Although high, these data rates were accommodated successfully in first generation digital audio applications such as CD and DAT. Unfortunately, second generation multimedia applications and wireless systems in particular are often subject to bandwidth and cost constraints that are incompatible with high data rates. Because of the success enjoyed by the first generation, however, end users have come to expect "CD-quality" audio reproduction from any digital system. Therefore, new network and wireless multimedia digital audio systems must reduce data rates without compromising reproduction quality. These and other considerations have motivated considerable research during the last decade towards formulation of compression schemes that can satisfy simultaneously the conflicting demands of high compression ratios and transparent reproduction quality for high-fidelity audio signals

Review of Standard Sound Quality Assessment Methods for the Transmitted and Processed Sounds

“…32, No.3 (2013) 215 기술의 발전으로 심리음향모델에 기반을 둔 지각 부 호화(perceptual coding) 방식의 압축을 이용한 오디오 의 전송 및 저장 기술이 널리 사용되고 있다. [10,11] 의 EBU의 주관 평가법에 대한 요약 및 Bech와 Zacharov [33] 의 주관 평가 이론, 방법론 그리고 응용에 재한 상세한 정리가 있다. 객관 평가법 리뷰에는 Rix 등, [34] Campbell 등 [35] 의 연구가 있으며, 종합적인 리 뷰에는 de Lima 등 …”

A robust audio watermarking scheme based on reduced singular value decomposition and distortion removal

“…Thus, we decided to remove these artefacts to achieve perceptual transparency independent of music style or genre. The psychoacoustic model [13] was used as a means to evaluate the perceptibility of the introduced distortion and, by extension, to detect any audible artefacts remaining.…”

“…This section will firstly give a concise introduction to the steps involved in deriving the NMR, which will then be adapted to our presented watermarking algorithm. The steps involved are [13]: where i denotes sub-band number, signal-to-mask ratio (SMR) is defined for each sub-band as the ratio of signal energy to LT min , SNR is defined for each sub-band as the ratio of signal energy to noise energy. A negative NMR indicates that the noise energy is below LT min .…”

“…As far as music is concerned, one of the most common attacks is compression. One very common technique is MP3 compression and surviving MP3 compression has therefore become an essential requirement for a watermarking scheme in the music domain [13]. This is due to the fact that MPEG-1 Layer III (MP3) and its variants have become the de facto standard for transmission and storage of compressed audio for both World Wide Web (WWW) and portable media applications [13].…”

“…One very common technique is MP3 compression and surviving MP3 compression has therefore become an essential requirement for a watermarking scheme in the music domain [13]. This is due to the fact that MPEG-1 Layer III (MP3) and its variants have become the de facto standard for transmission and storage of compressed audio for both World Wide Web (WWW) and portable media applications [13]. The difficulty when designing a watermark that can withstand MP3 compression is related to the fact that the MP3 algorithm nonlinearly modifies the spectrum based on a psychoacoustic model and the expected bit rate.…”