Pre-echo noise reduction in frequency-domain audio codecs

One of the most common yet detrimental compression artifacts in frequency-domain audio codecs is known as pre-echo, which is perceived as a brief noise preceding transient signals, and is discernable even without direct comparison to the original signal. Because of its substantial negative impact on audio quality, many techniques have been proposed to alleviate it, but not without effect on coding efficiency. This paper presents a novel method to reduce pre-echo noise using only information already available at the decoder, such as scale-factors, that allow an estimation of the quantization noise levels in each frequency band. Doing so allows the proposed method to reduce pre-echo noise based on a precise modeling of the quantization noise spread before the transient signal. This has shown to improve both the subjective and objective quality of the MPEG AAC codec, and requires no modifications to the existent standard-compliant encoders.