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Proprietary Low Bitrate Speech Codecs

The  Agora Labs SX-series speech coders utilize modern source coding techniques to compress human speech into acceptable data rates necessary for efficient transmission and storage. Traditionally speech required bandwidths of at least 64 kbits/sec for acceptable quality, rendering it too bandwidth intensive in environments where the data rates were limited. Agora Labs addresses this problem by offering speech coders at bitrates starting at 1200 bits/sec with compression ratios as high as 107:1.

The SX-series speech coders were originally developed at Lucent Technologies Bell Labs and were marketed for a time by elemedia. 

SX1200P Ultra Low Rate Speech Codec

The Agora Labs SX1200P speech codec provides speech at 1.2 kbits/sec making it the lowest bit rate coder available for internet telephony. Although suitable for a variety of applications, it is recommended for situations where ultra low bit rate is paramount. Applications such as videotelephony, voice messaging, and multimedia conferencing over narrowband channels are ideal for the SX1200P since it uses very little bandwidth. Modest memory and processing power requirements enable implementations of the coder on general purpose processors such as Intel's Pentium TM processor or on inexpensive DSPs.

Here are two voice samples that have been compressed and decompressed with this codec:

joy8k_12.wav  (file size 496K)
joevis8khp_12.wav (file size 380K)

SX2000P Very Low Rate Speech Codec

The Agora Labs SX2000P speech codec provides good speech quality at 2.0 kbits/sec making it an ideal choice for internet telephony and other very low bit rate applications such as videotelephony, voice messaging, and multimedia conferencing over narrowband channels. Even over 9.6 kbits/sec modem connections, the SX2000P leaves plenty of bandwidth available for browsing or collaborative computing. Modest memory and processing power requirements enable implementations of the coder on general purpose processors such as Intel's PentiumTM processor or on inexpensive DSPs.

Here are two voice samples that have been compressed and decompressed with this codec:

joy8k_20.wav (file size 498K)
joevis8khp_20.wav (file size 380K)

Sx7300P Toll Quality Low Complexity Speech Coder

The elemedia SX7300P codec gives speech quality comparable with ITU G.723 and G.729 Annex A but with enhanced performance in the presence of lost speech frames and at significantly lower complexity and lower cost. It operates at 7.3 kbps, uses a 15 mili-second frame with a 5 mili-second look ahead.

The elemedia SX8300P and SX9600P codecs are essentially the same as the SX7300P codec, only support 8.3 kbps and 9.6 kbps rates, respectively, and consequently provide slightly better quality than the SX7300P.

The SX7300P provides a high performance, low cost, low complexity solution ideal for speech transmission over the Internet or other packet networks. The coder offers close to toll quality speech and, with a rate of just 7.3 kbit/s, enables speech transmission over either V.34 or V.32bis modems. At V.34 data rates multiple speech channels or multimedia applications such as simultaneous voice and data may be supported on a single telephone line. The small frame size of the coder provides low end-to-end delay. A powerful frame reconstruction algorithm yields exceptionally robust performance in the presence of channel errors. The low delay characteristics and good tandeming performance make it ideal for multiparty conferencing. Modest memory and processing power requirements enable implementations of the coder in either Pentium or 486 environments or on inexpensive DSPs. The SX7300P offers speech quality comparable with ITU G.723 and G.729 Annex A with enhanced performance in the presence of lost speech frames and at significantly lower complexity and lower cost.

The next samples below demonstrate a comparison between the Agora Labs SX7300P speech coder and the ITU G.723 and G.729A speech coders under two packet loss conditions as described below. In each of the samples below, four sentences are spoken, each begins with a 400Hz tone and is then spoken five times. The original is first heard. Then the sentence is repeated four more times using different speech codecs. An ITU G.729A codec is used the second time the sentence is spoken; an ITU-T G.723.1 codec at 6.3kbps is used the third time the sentence is spoken; the Agora Labs SX7300P codec at 7.3kbps is used the fourth time the sentence is spoken; and an ITU-T G.723.1 codec at 5.3kbps is used the fifth time the sentence is spoken. (The packet loss comparison is for 60ms packet sizes). Again, here is the order of each sentence spoken:

 

Tone | Original | G.729A | G.723 (6.3kbps) | SX7300P | G.723 (5.3kbps)

 

 

Sx9600P Better Than Toll Quality Speech Coder

The SX9600P provides true toll quality at a bit rate of 9.6 kbit/s making it ideal for a broad range of applications. For corporate intranet or extranet applications where quality needs to be preserved, the SX9600P provides quality comparable to G.711 at a fraction of the bit rate.  For general internet applications, the coder provides excellent quality while still enabling speech transmission over either V.34 or V.32bis modems. At V.34 data rates, multiple speech channels or multimedia applications such as simultaneous voice and data may be supported on a single telephone line. The small frame size of the coder provides low end-to-end delay. A powerful frame reconstruction algorithm yields exceptionally robust performance in the presence of channel errors. The low delay characteristics and good tandeming performance make it ideal for multiparty conferencing. Modest memory and processing power requirements enable implementations of the coder in either PentiumTM or 486TM environments or on inexpensive DSPs. 

Customers normally license these products as object code software, they are available on the Pentium processor (IBM PC), PowerPC, MIPS, ARM and several popular DSP families.

Agora Labs is adding to their speech and audio codec product line, contact us if you don't see the codec you need!

 

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