Question: In the context of Enhanced Voice Services (EVS) codec, as per 3GPP standards, which of the following parameters is NOT used for classifying unvoiced frames in speech signals?
Option 1: Voicing measures
Option 2: Spectral tilt measures
Option 3: Harmonic-to-Noise Ratio (HNR) analysis
Option 4: Sudden energy increase from a low level to detect plosives
Explanation: The classification of unvoiced frames in the EVS codec relies on specific parameters. These include voicing measures, spectral tilt measures, and sudden energy increase from a low level. Harmonic-to-Noise Ratio (HNR) analysis, while useful in voice quality assessment for distinguishing between harmonic and noise components, is not used for unvoiced signal classification in this context.