This Recommendation defines do-no-harm (DNH) tests for network-based and terminal-based voice quality enhancement (VQE) functions and non-VQE functions. These tests are applicable to functions used in both fixed and mobile networks and are independent of transport technology (e.g., TDM, ATM and IP).

Where necessary, this Recommendation takes into account any similar tests that already exist in other Recommendations (e.g., [b-ITU-T G.160], [b-ITU-T G.168] and [b-ITU-T G.169]) and is applicable to both stand-alone VQE and non-VQE functions and VQE and non-VQE functions connected in tandem.

Where possible, the DNH tests defined in this Recommendation use standardized performance evaluation criteria (e.g., [ITU-T P.862] and [b-ITU-T P.863]) and cover all possible in-band audio signals including speech, voiceband data and network signalling tones. Each test has a well-defined test configuration and a set of requirements that allow repeatability and consistency of results between different test laboratories.

The following VQE and non-VQE functions are included in the scope for DNH:

- VQE functions:

° Echo cancellers including comfort noise injection 

° Noise reduction/cancellation functions

° Automatic gain/level control

- Non-VQE functions:

° De-jitter buffers

° Codecs

° Voice activity detection

° Silence suppression

Other functions which may be included are:

- Send or ingress (entering the network):

° Microphone array processing (MAP)

° High-frequency encoding (HFE)

° Equalization (EQ)

° Limiting (LM)

- Receive or egress (exiting the network):

° Bandwidth extension (BWE)

° Equalization (EQ)

° Noise compensation (NC; also referred to as ALE)

° Limiting (LM)

This Recommendation provides guidance on how to conduct DNH testing, including case studies, as specific examples.