AN3143 datasheet(4/13 Pages) STMICROELECTRONICS

Numer części	AN3143

Szczegółowy opis	Audio software codec for the STM8S

PDF	13 Pages

Scroll/Zoom	100%

Producent	STMICROELECTRONICS [STMicroelectronics]

Strona internetowa	http://www.st.com

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ADPCM codec

AN3143

4/13

Doc ID 17011 Rev 1

1.3

IMA ADPCM decompression

The IMA ADPCM decompression algorithm compresses samples which are stored as 4-bit

signed two’s complement values. The result is decompressed samples in linear 16-bit two’s

complement format.

The input sample (Sq) is dequantized using an inverse quantizer with an adapted step (q) to

obtain a difference (Sd). To reduce quantization errors, one half of the step size is added to

Sd. The resulting decompressed linear sample is the sum of Sd and the predicted sample

(Sp). As Sp is a simple zero order hold function, Sd is simply added to the previous output

value. The step size is adapted according to Sq. The decoder preconditions are that Sp is

cleared and that the quantization step is set to smallest one.

Figure 1.

ADPCM decoder

AN3143 Arkusz danych(PDF) 4 Page - STMicroelectronics