TrueVoice™ by Limes Audio

Acoustic Echo Cancellation Software

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TrueVoice™ AEC Software

The acoustic echo cancellation software TrueVoice™ by Limes Audio is powerful and flexible, the result of over a decade of research and practical application. The acoustic echo canceller in TrueVoice™ features full-duplex communication, fast convergence, stable operation and up to 512 ms filter length.

The software is a complete speech enhancement solution, that washes away disturbing echoes and noise, making your communication sound loud and clear, regardless of the distance and environment.

TrueVoice features

  • Acoustic Echo Cancellation
  • Full-duplex operation
  • Stereo AEC
  • Noise reduction
  • Automatic mic mixing
  • Beamforming
  • Automatic gain control
  • Equalizer
  • 512 ms echo tail
  • Fast convergence rate
  • High portability

TrueVoice is very modular and can be adapted to virtually all processing platforms. It has been deployed in deskphones, speakerphones, microphone mixers and intercom systems.


Schematic Description of TrueVoice AEC
Acoustic Echo Cancellation (AEC) software is used to remove echoes of the loudspeaker signal from a microphone. The TrueVoice™ software also removes noise and limits reverberation.

Acoustic Echo Cancellation

In hands-free communication, acoustic echoes appear when the signal played by the loudspeaker is recorded by the microphone and sent back to the far end speaker. Such echoes are likely to be very annoying and to drastically lower the subjective audio quality. Acoustic echo cancellers (AEC) attempt to remove acoustic echoes from the microphone signal by estimating the echo and subtracting it from the signal.

Acoustic echo cancellation is a complex problem, and AEC software must be carefully designed to work properly in different and challenging conditions. If the AEC algorithm is not properly designed it may fail to remove echoes and mute or distort parts of the speech signal, making sound quality even lower than it was.

Acoustic echo cancellers available in the market differ greatly in quality, adaptability, and computational requirements. At the same time, it is one of the critical determinants of audio quality in hands-free communication products. As such, the AEC solution used in a product must be carefully selected depending on the specific requirements and use cases of the product.

The TrueVoice Acoustic Echo Canceller Software

The TrueVoice AEC software excels in robustness and adaptability, performing well in situations where other solutions fail. TrueVoice can remove any acoustic echo from the signal using a combination of adaptive echo cancellation and non-linear processing (NLP). TrueVoice provides a loud and clear sound experience that lives up to high expectations and outperforms competitors.

Signal before TrueVoice echo cancellation & noise reduction
Audio signal polluted with noise, reverb and echoes
Signal after TrueVoice echo cancellation & noise reduction
TrueVoice processed audio signal: only speech remains

TrueVoice contains patented algorithms that are based on over 10 years of research and practical experience, and whose effectiveness have been proven through dozens of launched products.

TrueVoice is a highly portable software module that features a straightforward API, making it easy to integrate TrueVoice software with your other embedded software and hardware of choice. TrueVoice is written in C code and has already been ported to many different architectures, including ARM, x86, ADI SHARC and TI DSPs (floating-point and fix-point).

We have several demo kits that allow you to experience the power of the TrueVoice AEC first hand.

Automatic Microphone Mixing

Single-microphone hands-free products have lots of uses, but suffer in performance in larger rooms with many participants. Omnidirectional microphones take up sound from all directions and do not discriminate between the voice of the talker and other sounds such as reverberation (the voice of the talker reflected in the room) and background noise.

Using directional microphones, which primarily take up sound coming from one direction, allows speech to be clearly heard with less reverberation and noise. However, multiple microphones are needed in this case to cover the entire area of interest. Among these microphones, at any given moment the correct microphone(s) must be active in order to capture all present speech (possibly by several speakers) and filter out other sounds.

TrueVoice features automatic microphone mixing (AMM) that intelligently mixes the microphone signals (after applying AEC on each individual channel), and adjusts the gain level, in order to let speech be heard loud and clear while removing noise and speech reverberation. As such, TrueVoice is highly suitable for multi-microphone hands-free communication products designed for larger rooms and many participants.

Automatic Microphone Mixing
TrueVoice™ microphone mixing improves speech uptake and limits noise and reverb

Noise Reduction

Microphone noise reduction (NR) increases perceived speech quality and intelligibility, allowing hands-free communication systems to be used even in very noisy environments such as cars. TrueVoice features an adaptable noise reduction algorithm that can handle different types of noise while having minimal detrimental effect on the speech signal. The noise reduction of TrueVoice can be adjusted from 0 – 18 dB, by design or at installation, depending on what kind of environment the product is to be used in.

Noise reduction and the non-linear processing of the AEC result in changes to the noise level that can disturb the listener. TrueVoice adds a quiet comfort noise (CN) to the signal to counter this effect, resulting in a low-noise signal that is pleasant to the ear.

Application Areas

In any situation where a two-way speakerphone communication system is used, problems with echoes, noise, and room reverberation will be present. Types of these systems include:

  • Enterprise communication systems
    • Conference phones
    • Video conferencing equipment
  • Mobile communications devices
  • Consumer audio equipment
  • Smart home & security systems
  • Car infotainment systems

Put TrueVoice™ software in any of these products to achieve a loud and clear sound experience free of noise disturbances.