GAO Research Inc. recommends this high
performance G.726 vocoder which has been widely used in applications
such as speech transmission over digital networks, video conferencing,
multimedia and ISDN communications. This G.726 vocoder complies with
the ITU-T standard and operates at 40, 32, 24, and 16kbps. It was
introduced to supersede both G.721, which covered ADPCM at 32 kbit/s,
and G.723, which described ADPCM for 24 and 40 kbit/s. G.726 also
introduced a new 16 kbit/s rate. The four bit rates associated with
G.726 are often referred to by the bit size of a sample, which are
2-bits, 3-bits, 4-bits, and 5-bits respectively.
This vocoder converts a 64Kbps A-law or μ-law PCM channel to or
from a 40, 32, 24 or 16kbps channel.The conversion is applied to the
PCM bit stream using an ADPCM transcoding technique. Thus, the scheme
has switchable transmission rates providing 4kHz of audio bandwidth. It
encodes 13 or 14-bit PCM samples or 8-bit, A-law or μ-law encoded data
into 2, 3, 4, or 5-bit code words. Since the algorithm encodes one
sample at a time, the coding or decoding delay is zero which ensures
robust, quality audio.
All GAO Research’s speech software has
passed the test vectors specified by the ITU GAO also adheres to
stringent quality control procedures, which is reflected in the well
structured code, detailed design documentation, and well-defined design
and test plans. This ensures ease of integration, easy maintenance and
a smooth upgrade path for further generation customer products.
