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G.168 Line Echo Canceller Software

Line Echo Cancellation Diagram

G.168 Line Echo Canceller software reduces line echo for superior speech enhancement

G.168 Line Echo Canceller Software is fully compliant with ITU G.168 specification as well as satisfies our own rigorous proprietary tests. Our line echo canceller software is designed to pass and exceed requirements using any of the G.168-2012 echo path models as well as applicable customer models. VOCAL provides robust echo cancellation and noise reduction algorithms that can be configured to significantly reduce echoes and remove residual noise from the voice signal. Contact us to discuss your voice application requirements.

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VOCAL has developed a range of line / network echo canceller solutions which are installed world-wide and used in the public telephone system and TDM echo cancellation circuits, VoIP applications, and many other types of manufactured products. VOCAL’s experts can help you select and configure the algorithms that best fit your needs.

The G.168 Line Echo Cancellation algorithm is available standalone, as part of an embedded library, or with a complete ATA/VoIP Gateway solution. Our G.168 software is optimized for DSPs and conventional processors from TI, ADI, ARM, AMD, Intel and other leading vendors. Custom solutions are also available.

G.168 Line Echo Canceller

The G.168 specification was developed to address and standardize the performance for line echo cancellation in the PSTN. G.168 strictly limits the convergence time, allowed residual echo, tolerance for varying signal levels, and allowed divergence in the presence of destabilizing narrow-band energy. The line echo cancellation requirements also specify the performance of any additional non-linear processing such as clamping and/or suppression, ability to handle data communication, and disabling signals such as the modem ‘ANSam’ tone. Addendums to the original G.168 specification from 1997 further restricted and quantified the requirements for line echo cancellation algorithm compliance.

G.168 Line Echo Cancellation
 G.168 Line Echo Canceller must be placed in the 4-wire portion of a circuit (which may be an individual circuit path or a path carrying a multiplexed signal). While intended for use in the PSTN, the extremely high performance and versatility of G.168 compliant algorithms allow them to be used in a wide variety of applications for line noise cancellation. For VoIP and embedded devices, the line echo canceller may be placed after an audio codec (such as G.711, G.722, G.723.1, G.726, G.728, G.729, G.729A, G.729AB, GSM, MELP, etc.) to reduce the echo from local or customer hardware.

Like all of VOCAL’s software libraries, our G.168 line echo cancellation algorithm is available in a variety of forms, including ANSI C and assembly language implementations optimized for leading DSP architectures. The line echo canceller libraries are modular and can be executed standalone with its own microkernel or as a single task under a variety of operating systems.


  • Fully compliant with ITU G.168 Recommendation
  • Rapid convergence
  • Double talk detection
  • Low divergence during double talk
  • Adjustable tail length to 32 msec for full compliance
  • Adjustable tail length to 128 msec with restricted compliance
  • Proper operation during facsimile and low speed (<9.6 kbit/s) voice-band data transmissions
  • Disables automatically in the presence of ANSam
  • Excellent tone rejection and narrow band stability
  • Non-linear processing (NLP) with Comfort Noise Generator (CNG)
  • Supports user callable functions
  • Utilizes Normalized LMS (NLMS)
  • Tone detector and hold release logic
  • Supports multiple channels
  • Easily portable, re-entrant and re-locatable code

G.168 Line Echo Canceller Test Compliance

VOCAL’s line echo cancellation modules pass the standard ITU G.168 Test Suite:

  • Test No. 2 Convergence and Steady state residual and returned echo level tests
  • Test 2A Convergence test with NLP enabled
  • Test 2B Convergence test with NLP disabled
  • Test 2C Convergence test in the presence of background noise
  • Test No. 3 Performance under conditions of double talk
  • Test 3A Double talk test with low cancelled-end levels
  • Test 3B Double talk test with high cancelled-end levels
  • Test 3C Double talk test under simulated conversation
  • Test No. 4 Leak rate test
  • Test No. 5 – Infinite return loss convergence test
  • Test No. 6 – Non-divergence on narrow-band signals
  • Test No. 7 – Stability test
  • Test No. 9 – Comfort noise test
  • Test No. 10 – Facsimile test during call establishment phase
  • Test No. 10A – Canceller operation on the calling station side
  • Test No. 10B – Canceller operation on the called station side
  • Test No. 14 – Performance with V.Series Low-speed Data Modems

Proprietary G.168 Line Echo Canceller Test Compliance

As an experienced leader in this field, VOCAL has identified shortcomings in the G.168 standard and has implemented several additional test sets to guarantee world-class performance of our G.168 line echo canceller software in the harshest acoustic environments. All of our line echo cancellation modules must pass these VOCAL specific tests in addition to the standard ITU G.168 Test Suite, as well as undergo voice testing in our labs.

  • VOCAL Test 2D – improved echo power test
  • VOCAL Test 3D – double talk in the presence of tones
  • VOCAL Test 5D – improved line change detection
  • VOCAL Test 7D – improved narrow band rejection
  • VOCAL Test 9D – improved comfort noise tracking
  • VOCAL Test 9E – comfort noise tracking during singletalk
  • VOCAL Test 9F – comfort noise tracking during doubletalk
  • VOCAL Test 9G – comfort noise transitions
  • VOCAL Test 21 – ANSam detection

More Information


supported platforms

VOCAL’s software is available for the following platforms. Please contact us for specific G.168 supported platforms and performance data.

Processors Operating Systems
  • Texas Instruments – C6xx (TMS320C62x, TMS320C64x, TMS320C645x, TMS320C66x, TMS320C67x), DaVinci, OMAP, C5xx (TMS320C54x, TMS320C55x)
  • Analog Devices – Blackfin, ADSP-21xx, TigerSHARC, SHARC
  • PowerPC, PowerQUICC
  • MIPS – MIPS32, MIPS64, MIPS4Kc
  • ARM – ARM7, ARM9, ARM9E, ARM10E, ARM11, StrongARM, ARM Cortex-A8/A9, Cortex-M3/M4
  • Intel / AMD – x86, x64 (both 32 and 64 bit modes)
  • Linux, uClinux, BSD, Unix
  • Microsoft Windows ACM / RTC / CE / Mobile
  • Apple iOS / iPhone / iPad & MacOS
  • eCOS / eCOSPro
  • Google Android
  • Green Hills Integrity
  • Micrium μCOS
  • Symbian
  • Wind River VxWorks


ITU Recommendation G.168

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