A speech-signal-processing-circuit configured to receive a time-frequency-domain-reference-speech-signal and a time-frequency-domain-degraded-speech-signal, wherein each of the time-frequency-domain-reference-speech-signal and the time-frequency-domain-degraded-speech-signal comprises a plurality of frames of data, wherein: the time-frequency-domain-reference-speech-signal is in the time-frequency domain and comprises: an upper-band-reference-component with frequencies that are greater than a frequency-threshold-value; and a lower-band-reference-component with frequencies that are less than the frequency-threshold-value; the time-frequency-domain-degraded-speech-signal is in the time-frequency domain and comprises: an upper-band-degraded-component with frequencies that are greater than the frequency-threshold-value; and a lower-band-degraded-component with frequencies that are less than the frequency-threshold-value; the speech-signal-processing-circuit comprises: a disturbance calculator configured to determine one or more spectral-balance-ratio features based on the time-frequency-domain-reference-speech-signal and the time-frequency-domain-degraded-speech-signal by: (i) for each of a plurality of frames: determining a reference-ratio based on the ratio of (i) the upper-band-reference-component to (ii) the lower-band-reference-component; determining a degraded-ratio based on the ratio of (i) the upper-band-degraded-component to (ii) the lower-band-degraded-component; and determining a spectral-balance-ratio based on the ratio of the reference-ratio to the degraded-ratio; and (ii) determining the one or more SBR-features based on the spectral-balance-ratio for the plurality of frames; and a score-evaluation-block configured to determine an output-score for the degraded-speech-signal based on the SBR-features. the time-frequency-domain-reference-speech-signal is in the time-frequency domain and comprises: an upper-band-reference-component with frequencies that are greater than a frequency-threshold-value; and a lower-band-reference-component with frequencies that are less than the frequency-threshold-value; an upper-band-reference-component with frequencies that are greater than a frequency-threshold-value; and a lower-band-reference-component with frequencies that are less than the frequency-threshold-value; the time-frequency-domain-degraded-speech-signal is in the time-frequency domain and comprises: an upper-band-degraded-component with frequencies that are greater than the frequency-threshold-value; and a lower-band-degraded-component with frequencies that are less than the frequency-threshold-value; an upper-band-degraded-component with frequencies that are greater than the frequency-threshold-value; and a lower-band-degraded-component with frequencies that are less than the frequency-threshold-value; the speech-signal-processing-circuit comprises: a disturbance calculator configured to determine one or more spectral-balance-ratio features based on the time-frequency-domain-reference-speech-signal and the time-frequency-domain-degraded-speech-signal by: (i) for each of a plurality of frames: determining a reference-ratio based on the ratio of (i) the upper-band-reference-component to (ii) the lower-band-reference-component; determining a degraded-ratio based on the ratio of (i) the upper-band-degraded-component to (ii) the lower-band-degraded-component; and determining a spectral-balance-ratio based on the ratio of the reference-ratio to the degraded-ratio; and (ii) determining the one or more SBR-features based on the spectral-balance-ratio for the plurality of frames; and a score-evaluation-block configured to determine an output-score for the degraded-speech-signal based on the SBR-features. a disturbance calculator configured to determine one or more spectral-balance-ratio features based on the time-frequency-domain-reference-speech-signal and the time-frequency-domain-degraded-speech-signal by: (i) for each of a plurality of frames: determining a reference-ratio based on the ratio of (i) the upper-band-reference-component to (ii) the lower-band-reference-component; determining a degraded-ratio based on the ratio of (i) the upper-band-degraded-component to (ii) the lower-band-degraded-component; and determining a spectral-balance-ratio based on the ratio of the reference-ratio to the degraded-ratio; and (ii) determining the one or more SBR-features based on the spectral-balance-ratio for the plurality of frames; and (i) for each of a plurality of frames: determining a reference-ratio based on the ratio of (i) the upper-band-reference-component to (ii) the lower-band-reference-component; determining a degraded-ratio based on the ratio of (i) the upper-band-degraded-component to (ii) the lower-band-degraded-component; and determining a spectral-balance-ratio based on the ratio of the reference-ratio to the degraded-ratio; and determining a reference-ratio based on the ratio of (i) the upper-band-reference-component to (ii) the lower-band-reference-component; determining a degraded-ratio based on the ratio of (i) the upper-band-degraded-component to (ii) the lower-band-degraded-component; and determining a spectral-balance-ratio based on the ratio of the reference-ratio to the degraded-ratio; and (ii) determining the one or more SBR-features based on the spectral-balance-ratio for the plurality of frames; and a score-evaluation-block configured to determine an output-score for the degraded-speech-signal based on the SBR-features.