Automatic Sound Signals Quality Estimation (2/4)
To Audio Codecs Quality Analyzer page
Introduced System General Concept
Generator of test signals allows sound signal forming according to one of the sound flow models. It can be either a particularized set of sound signals or a signal, received in output of statistical speech model. Generator’s signal can either be saved for follow-up usage or be exposed to processing and estimation. Bank of signals stores sound data, received as a result of signals’ generator work or from some external sources.
Accordingly, an input of estimation block is a signal of generator directly or one of the bank of signals. Test signal is the input of the synchronizer or of the device under test, which can be for example, a vocoder or a communication channel. The output signal of the device under test is an input of synchronizer also.
The synchronizer matches in time an initial signal and a processed signal. The synchronized signals in chunks input in analytical module, which determines the degree of similarity for signals and issues the quality estimation as the measure of similarity between the initial and the processed signals.
Implementation
Algorithms described are implemented in Sevana Audio Codecs Analyzer for vocoder quality estimation and comparison of external initial signals and signals under test.
As the external signals arbitrary signals recorded with the sampling frequency of 8 kHz and the capacity of samples equal 16 bits can be used. Supposed, the signal under test is received from an initial signal as a result of some transformations (for example, compression/restoration, transmission through communication channels, filtration).
As internal initial signals (i.e. signals, which the user of the program has no access to) the signals generated according to the proprietary noise model and the signals, generated on the basis of the statistic model.
Internal input signals of sound data to the system, are implemented as DLL. One can use both DLLs provided within Sevana Audio Codecs Analyzer or developed by the others. The signal processed by means of methods contained in DLL is consider as the signal under test and is exposed to the proprietary quality estimation procedure.
Advantages
• It is a universal tool since it allows judging the quality of signals from various sources and processed in different ways;
• One can optimize quality estimation signal depending on the purposes:
- in speed (for example, it is possible to receive rough estimation quickly);
- in signal type (using different bands for speech signals and sound signals in general);
• Resulting estimations correlate well with that of МОS;
• Quality estimations received for speech signals can be translated in values of various kinds of intelligibility.
Test results
The table above represents quality estimations of several standard vocoders, received on various test signals using the proprietary method and Sevana Audio Codecs Analyzer. The table contains MOS estimations for comparison.
Estimations under the assumption, that bands are of equal probability, are in the column with «-» symbol and the estimation received under taking into account the coefficients of importance are in the column with «Vc».
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