Extending the Bandwidth of NarrowBand Speech Using Cepstral Linear Prediction
7. Subjective Results
Subjective tests were conducted through a random pool of 5 listeners from the Nanyang Technological University's Centre for Signal Processing. The results are presented herein. Table 2 associates the ratings with the level of distortion perceptually heard by the listeners during the test while Table 3 shows the end results. It is clear that the algorithm achieves its objective in enhancing the quality of perceived speech from the original narrow band speech signal.
Table 2: MOS Rating Legend
| Rating | Speech Quality | Level of Distortion |
| 5 | Excellent | Imperceptible |
| 4 | Good | Just perceptible |
| 3 | Fair | Perceptible |
| 2 | Poor | Annoying |
| 1 | Bad | Unsatisfactory |
Table 3: Tabulated MOS Ratings
| Speech | 1 | 2 | 3 | 4 | 5 | 6 | Average |
| Listener 1 | |||||||
| Original Speech | 5 | 5 | 5 | 5 | 5 | 5 | 5.0 |
| Narrowband Speech | 3 | 3 | 3 | 3 | 3 | 3 | 3.0 |
| Enhanced Cepstral | 4 | 3 | 4 | 3 | 3 | 3 | 3.5 |
| Listener 2 | |||||||
| Original Speech | 4 | 4 | 4 | 5 | 5 | 5 | 4.5 |
| Narrowband Speech | 3 | 3 | 3 | 3 | 3 | 3 | 3.0 |
| Enhanced Cepstral | 3 | 3 | 4 | 3 | 4 | 4 | 3.5 |
| Listener 3 | |||||||
| Original Speech | 5 | 5 | 5 | 5 | 5 | 5 | 5.0 |
| Narrowband Speech | 3 | 3 | 3 | 3 | 3 | 3 | 3.0 |
| Enhanced Cepstral | 3 | 3 | 3 | 4 | 3 | 4 | 3.33 |
| Listener 4 | |||||||
| Original Speech | 5 | 5 | 5 | 5 | 5 | 5 | 5.0 |
| Narrowband Speech | 3 | 3 | 3 | 3 | 3 | 3 | 3.0 |
| Enhanced Cepstral | 4 | 3 | 4 | 4 | 4 | 3 | 3.5 |
| Listener 5 | |||||||
| Original Speech | 5 | 5 | 5 | 5 | 5 | 5 | 5.0 |
| Narrowband Speech | 3 | 3 | 3 | 3 | 3 | 3 | 3.0 |
| Enhanced Cepstral | 4 | 3 | 4 | 4 | 4 | 4 | 3.83 |
| Averages | |||||||
| Average MOS for Original Speech | 4.90 | ||||||
| Average MOS for Narrowband Speech | 3.0 | ||||||
| Average MOS for Enhanced Cepstral speech | 3.53 | ||||||
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