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Introduction
Functionality
Scientific Background
AQuA Command Line parameters
AQuA Command Line usage
Analysis of possible reasons for voice and audio quality loss
Visualizing signals spectrum for analysis
AQuA Online
AQuA Benefits

AQuA – Audio Quality Analyzer page
Download AQuA Manual as PDF

Analysis of possible reasons for voice and audio quality loss

Besides audio quality score AQuA gives a possibility to analyze and determine possible reasons that caused audio signal degradation. Software automatically prepares analysis results that can be returned as a string or stored in a log file depending on the chosen option.

Additional audio quality metrics returned by the system may not look trivial to understand and this chapter is devoted to the main principles of how these metrics are built and how one can interpret them.

AQuA returns additional metrics only in the case when they are out of range for their “typical values” (exception Signal/Noise Ratio (SNR) that is always present in the report). In case the metrics are within the range the system returns “Cannot determine the major reason for audio quality loss”.

Signal/Noise Ratio (SNR)

These metrics represent SNR both in the original and degraded files and

Source SNR : ХХ.ХХ.
Degradated SNR : ХХ.ХХ.
These metrics show the signal/noise ratio of the original and degraded signals. Typically signal quality gets lower when SNR value decreases.

Duration distortion

This metric represents continuity of compared audio files. Ideally amount of audio data in the original signal and file under test should be the same. During audio processing or transfer over communication channels audio fragments may be lost as well as inserted into the audio. If such audio degradation took place then value of this metric is lower than 100. The bigger the difference the stronger the degradation, however, this metric does not consider possible starting pauses.

When the value is less than 100% this means that audio data was lost and analysis result will be:

Audio shrinking corresponds to ХХ.ХХ percent.

where ХХ.ХХ corresponds to deviation from 100%.

When the actual value is more than 100% this means that data was inserted and analysis result will be:

Audio stretching corresponds to ХХ.ХХ percent.

where ХХ.ХХ corresponds to deviation from 100%.

Tolerance range for this value is set to 100% ± 1%.

Delay/Advancing of audio signal activity

This metric represents signal shift in test file compared to the original and determines how much active level of the test signal delays/advances active level of the etalon (original) signal. When it is delayed analysis returns the following

Signal delayed by ХХ.ХХ ms.

where ХХ.ХХ is delay time in milliseconds. Correspondently, when the signal advances the original the return string is:

Signal advances the original by -ХХ.ХХ ms.

where ХХ.ХХ is advancing time.

Tolerance range for this value is interval of ±50 ms.

Corrupted signal spectrum

This represents a set of metrics reflecting differences in integral energy spectrums of the original signal and audio under test. If overall spectrums difference is more than 15% than analysis returns the following string:

Corrupted signal spectrum.

If difference in spectrums is multidirectional (goes both into positive and negative zones) analysis returns the following string:

Vibration along the whole spectrum [-ХХ.XX, YY.YY] %

where ХХ.XX and YY.YY are deviations to negative and positive zones correspondently. Tolerance range of the deviation is ±5%.

If spectrum distortions are unidirectional (only negative or only positive) analysis returns this string:

Amplification approaches YY.YY %

When distortions are positive, or

Attenuation approaches ХХ.XX %

when distortions are negative.

Other metrics returned by analysis correspond to distortions occurred in different frequency groups. Analysis of different frequency bands performs in a similar manner to spectrum analysis. When talking about frequency bands in question we consider:
Low frequencies – below 1000 Hz
Medium frequencies – from 1000 Hz to 3000 Hz
High frequencies are those that are greater than 3000 Hz

When analyzing frequency bands we use other value tolerance ranges. Distortion in low frequencies is considered when they are greater than 5%, in medium frequencies – 10% and in high frequencies – 30%.

Multidirectional spectrum changes (vibration) is considered when they are greater than 2.5% in low frequencies, 7% in medium frequencies and 15% in high frequencies.

Unidirectional distortions (no matter positive or negative) are considered when they are greater than 5% in low frequencies, 10% in medium frequencies and 25% in high frequencies.

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