Influence of Compression Ratio on Temporal Envelope Preservation in Speech: An Acoustic Simulation Study

Introduction: Temporal envelope cues play a crucial role in speech perception, particularly for individuals with sensorineural hearing loss who rely heavily on these cues due to reduced access to fine spectral detail. Wide dynamic range compression (WDRC) is widely used in hearing aids to improve audibility; however, inappropriate compression settings may distort the temporal envelope of speech. Objective evidence examining the influence of compression ratio on temporal envelope preservation remains limited. Material and Method: An acoustic simulation study was conducted using 20 prerecorded adult speech samples. All speech signals were RMS-normalized and processed in MATLAB using simulated WDRC with compression ratios of 1:1 (linear), 1.5:1, 2:1, 3:1, and 4:1, while maintaining constant compression threshold and time constants. Temporal envelopes were extracted using the Hilbert transform and low-pass filtered at 50 Hz. Envelope preservation was quantified using Pearson correlation coefficients and root mean square error (RMSE). Repeated-measures analysis of variance was used for statistical analysis. Result: Envelope correlation decreased systematically with increasing compression ratio, whereas RMSE increased correspondingly. Linear and mildly compressive processing demonstrated higher envelope similarity, while marked envelope distortion was observed at compression ratios of 3:1 and above. Compression ratio had a significant effect on both envelope correlation and RMSE (p < 0.001). Conclusion: Higher compression ratios substantially degrade temporal envelope preservation in speech signals. Mild compression preserves envelope structure more effectively than aggressive compression. These findings highlight the importance of considering temporal envelope integrity when selecting compression parameters in hearing-aid signal processing.