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SILK Codec & SILK Voice Codec

VOCAL’s SILK voice codec algorithm is optimized to run on major DSPs and processors as a real-time implementation that can be configured by developers to support internet wideband audio multichannel applications. Our SILK speech compression is available for licensing as a standalone algorithm, as part of a modular software library suite, as well as with a VoIP stack for different integration options with user applications. Custom designs are also available. Contact us to discuss your voice application requirements.

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SILK vocoder is optimized for execution in ANSI C and on leading DSP architectures from TI, ADI, AMD, ARM, MIPS, Intel and others. It can be integrated with our Acoustic Echo Canceller (AEC), G.168 echo canceller, noise reduction algorithms, or any other telephony product, as well as with our VoIP stack.

SILK Codec

The SILK vocoder is designed by Skype as an internet wideband audio codec for use in Voice over IP (VoIP). It operates at four different sampling rates: 8 kHz narrowband, 12 kHz mediumband, 16 kHz wideband, and 24 kHz superwideband. These allow for the capture of higher frequencies, which provide fuller sound, while also allowing interoperability with the Public Switched Telephone Network (PSTN). SILK has automatic detection of superwideband audio and can downsample to wideband if there is no benefit to the inclusion of the higher frequencies.

SILK has a variable bitrate (VBR) that can be set between 6 and 40 kbps, with higher bitrates providing better sound quality due to less quantization noise. SILK operates on 20 ms frames with a 5ms look ahead which causes a 25 ms algorithmic delay. The compressed audio is contained in packets of 20, 40, 60, 80 or 100 ms. Larger packets can provide a lower effective bitrate due to IP overhead per packet and certain parameters being conditionally encoded after the first frame per packet. Larger packets also cause longer delays and are more prone to errors due to lost packets. SILK has Low Bite Rate Redundancy (LBRR), also called Forward Error Correction (FEC), which makes it robust to packet loss.

SILK has three complexity settings: low, medium, and high. These control the order of the filters used for pitch estimation and noise shaping ans the number of stages used in the quantization of the noise shape parameters, the Long Term Prediction (LTP) coefficients, and the Normalized Line Spectral Frequencies (NLSF). This allows SILK to take advantage of today’s powerful processors while not abandoning older processors.



VOCAL’s speech coders are available for the following platforms:

  • Texas Instruments - C6000 (TMS320C62x, TMS320C64x, TMS320C645x, TMS320C66x, TMS320C67x), DaVinci, OMAP, C5000 (TMS320C54x, TMS320C55x)
  • Analog Devices – Blackfin, TigerSHARC, SHARC
  • PowerPC
  • MIPS – MIPS32, MIPS64, MIPS4Kc
  • ARM – ARM7, ARM9, ARM9E, ARM10E, ARM11, StrongARM, ARM Cortex-A8, Cortex-M1
  • Intel / AMD x86, x64 (both 32 and 64 bit modes)

Please contact us for specific SILK voice codec supported platforms.

Operating Systems

VOCAL’s SILK voice codec software is available for the following Operating Systems:

  • Google Android
  • Apple iOS / iPhone / iPad & MacOS
  • Unix,  Linux, μClinux, BSD
  • Microsoft Windows ACM / RTC / CE / Mobile
  • Symbian
  • eCOS / eCOSPro
  • Wind River VxWorks
  • Green Hills Integrity
  • Micrium μCOS

Please contact us for other supported Operating Systems.

VOCAL Technologies, Ltd.
520 Lee Entrance, Suite 202
Amherst, New York 14228
Phone: +1-716-688-4675
Fax: +1-716-639-0713