Lossless compression

Definition of Lossless Compression

The so-called lossless compression format, as the name suggests, is an audio format that compresses the sound signal without any loss. Common formats such as MP3, WMA, etc. are lossy compression formats, compared to WAV files as the source, they have a considerable degree of signal loss, which is the root cause of their ability to achieve a compression rate of 10%. Lossless compression format, it is like using Zip or RAR such compression software to compress the audio signal, the compression format obtained is reduced to a WAV file, and as the source of the WAV file is exactly the same! But if you use Zip or RAR to compress a WAV file, you have to decompress the compressed package before you can play it. Lossless compression format can be played in real time directly through the playback software, and it is exactly the same as MP3 and other lossy formats. In short, lossless compression is a format that can reduce the size of WAV files without sacrificing any audio signal.

In lossless audio compression, a common approach is to use a combination of linear prediction and entropy coding. The linear predictor first removes the redundancy in the input data and generates prediction residuals, which are then encoded by the entropy encoder. Linear predictive coding LPC and Huffman coding are the most commonly used tools for prediction and entropy coding.

IEEE 1857.2 lossless audio compression system consists of encoder and decoder. In encoding, the input audio samples are first processed by a predictor, which removes correlations in the input audio samples and generates prediction residuals. Then the prediction residuals go through a preprocessing step and the dynamic range of the signal is reduced, in other words the amplitude envelope of the signal is flattened. The flattened prediction residuals are subsequently encoded by an entropy encoder into a lossless bitstream. In decoding, the reverse process is performed, where the lossless bit stream is entropy decoded, post-processed (de-flattened) and losslessly reconstructed into a decoded signal, which is an exact copy of the original input audio.

In IEEE 1857.2, the fast algorithm is used in the algorithm encoder. When encoding each frame, the parameter index is first differentially encoded and then arithmetic encoded. The arithmetic encoder then encodes the predicted residuals in the frame using a proportional probability table.

vantage point

• 100% preservation, without any signal loss.
• High sound quality, notaffectedbythe signal source.
• Convenient conversion.

disvantage point

• Takes up a lot of space and doesn’t have a high compression ratio.

2 Lack of hardware support.

Your task

Which audio file formats are lossless compression?

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