spectral band replication (audio codec) (SBR)

Audio codecs use various compression algorithms as well as various other techniques to achieve the highest possible sound quality at low bit rates while keeping file sizes as small as possible. The SBR(Spectral Band Replication) method, which is used in Advanced Audio Coding( AAC), in aacPlus and mp3pro, is a bandwidth expansion method that is characterized by high sound and speech quality at low bit rates.

The SBR method applies to sounds above 5 kHz, which are extracted from normal decoding and reconstructed using Spectral Band Replication. This reconstruction means that the high tones, which represent a larger amount of data, do not need to be transmitted as well. The sound reconstruction is based on the lower frequencies generated by the normal decoder. In order that a proper reconstruction of the audio signals can take place, information about the envelope of the uncoded time signal is transmitted in addition to the transmitted audio data. The additional information can be transmitted with about 2 kbit/s. The receiver can use this control data to harmonically extend the audio signal. The reconstruction works very efficiently with the harmonics and allows the correct reconstruction of the waveform with respect to its time and frequency behavior.