# Digital Human Technology in E-Learning: Custom Content Solutions
## 6 Evaluation and Discussion
### Objective Evaluation
#### 6.1.2 Audio Quality  
We evaluate the generated speech using four metrics: (1) the automatic speech recognition (ASR) score, which measures intelligibility by comparing recognized text with the original text; (2) pitch, which influences the perception of highness or lowness of a tone and is determined by the fundamental frequency of the sound wave; (3) speech rate (also referred to as tempo), which quantifies the rhythm or speed of speech in terms of words or syllables per minute; and (4) short-time energy (STE), which captures temporal variations in speech loudness. Table 5 details these metrics and their computational procedures.  
Pitch provides insights into the quality of a sound, aids in differentiating tones and accents, and highlights speaker-specific characteristics [45]. Speech rate directly affects segmentation, word alignment, and overall recognition accuracy; accurate tempo analysis enables ASR systems to adapt to varying speaking styles. Lastly, short-time energy is commonly used to segment a voice signal by detecting word boundaries, and by analyzing energy variations over short time frames, it improves transcription precision [46].  
From the results shown in Table 6, the \"Casual\" style achieves the highest ASR Score, 66.25, whereas the \"Formal\" and \"Keypoints\" styles score slightly lower at 62.20 and 61.25, respectively. Since the ASR score, pitch, and short-time energy values are normalized on a 0-100 scale, higher values correspond to better performance. All three styles share the same pitch value, 100, suggesting comparable tonal ranges.  
\begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline
**Metric Name** & **Calculation Method** & **Meaning** \\ \hline Semantic Matching Score [42] & Compare the semantics of the original text with the test text, typically using text classification methods to verify whether the test text remains faithful to the original meaning. & Indicates how closely the test text aligns with the source semantics; higher scores suggest stronger consistency. \\ \hline Concept Contradictions [43] & Divide the test text into multiple sentences and compare each pair to detect semantic contradictions. Identifying contradictory relationships reveals logical conflicts or semantic inconsistencies. & Helps discover potential logical or conceptual conflicts within the test text, thereby improving overall accuracy and coherence. \\ \hline Sentence Coherence [44] & Extract semantic vectors for each sentence in the test text, compute adjacency (e.g., cosine) similarity between neighboring sentences, and derive an average coherence score. & Evaluates whether sentence-to-sentence logical and semantic transitions are smooth. Higher scores indicate more natural flow and coherence throughout the text. \\ \hline \end{tabular}
\end{table}
Table 4: Semantic text evaluation metrics.  
Tempo, measured in words or syllables per minute, does not have a strictly linear relationship with quality. Typical teacher speaking speeds range from 50 to 200 words per minute, and all three styles fall within this interval. The \"Keypoints\" style is delivered fastest at 123.05, followed by \"Formal\" at 117.45, and \"Casual\" at 86.13. In terms of short-time energy, the \"Casual\" style exhibits the highest value, 40.445, indicating stronger loudness variation compared to \"Formal\" at 35.91 and \"Keypoints\" at 39.73.