G711 Codec

Description

The G711 Codec block is a logarithmic scalar quantizer designed for narrowband speech. Narrowband speech is defined as a voice signal with an analog bandwidth of 4 kHz and a Nyquist sampling frequency of 8 kHz. The block quantizes a narrowband speech input signal so that it can be transmitted using only 8-bits. The G711 Codec block has three modes of operation: encoding, decoding, and conversion. You can choose the block's mode of operation by setting the Mode parameter.

If, for the Mode parameter, you choose Encode PCM to A-law, the block assumes that the linear PCM input signal has a dynamic range of 13 bits. Because the block always operates in saturation mode, it assigns any input value above $$2^{12}-1$$ to $$2^{12}-1$$ and any input value below $$-2^{12}$$ to $$-2^{12}$$. The block implements an A-law quantizer on the input signal and outputs A-law index values. When you choose Encode PCM to mu-law, the block assumes that the linear PCM input signal has a dynamic range of 14 bits. Because the block always operates in saturation mode, it assigns any input value above $$2^{13}-1$$ to $$2^{13}-1$$ and any input value below $$-2^{13}$$ to $$-2^{13}$$. The block implements a mu-law quantizer on the input signal and outputs mu-law index values.

If, for the Mode parameter, you choose Decode A-law to PCM, the block decodes the input A-law index values into quantized output values using an A-law lookup table. When you choose Decode mu-law to PCM, the block decodes the input mu-law index values into quantized output values using a mu-law lookup table.

If, for the Mode parameter, you choose Convert A-law to mu-law, the block converts the input A-law index values to mu-law index values. When you choose Convert mu-law to A-law, the block converts the input mu-law index values to A-law index values.

If, for the Mode parameter, you choose Encode PCM to A-law or Encode PCM to mu-law, the Overflow diagnostic parameter appears on the block parameters dialog box. Use this parameter to determine the behavior of the block when overflow occurs. The following options are available:

Parameters

References

ITU-T Recommendation G.711, “Pulse Code Modulation (PCM) of Voice Frequencies,” General Aspects of Digital Transmission Systems; Terminal Equipments, International Telecommunication Union (ITU), 1993.

Supported Data Types

See Also