Effects of Independent Dynamic Range Compression of Speech and Music Signals on Sound Quality

Purpose: This study aimed to compare the effects of independent dynamic range compression (independent DRC) and conventional mixed-signal dynamic range compression (conventional DRC) on the sound quality of speech and music, in an ideal condition where the individual sound sources are available to the compressor. The hypothesis is that independent DRC optimized for individual signals yields higher sound quality ratings than conventional DRC optimized for a single signal. Method: Participants were 15 young adults with audiometrically normal hearing. Stimuli included a 10-s-long spontaneous speech sample spoken by a female talker mixed with a classical music excerpt. The speech level was fixed at 65 dBA, and the music level was varied to achieve three speech-to-background ratios (SBRs; −10, 0, and 10 dB). A hearing aid simulator applied frequency-specific gain for a standard mild–moderate hearing loss with three amplification strategies: (a) conventional DRC—speech and music were compressed with a 50-ms release time after the signals were mixed; (b) independent DRC—speech was compressed with a 50-ms release time, and music was independently compressed with a 4,000-ms release before the signals were mixed; and (c) linear amplification (control condition)—stimuli were processed with linear amplification, before or after mixing. The participants rated sound quality across four scales: overall sound quality, speech clarity, speech naturalness, and music naturalness. Results: Independent DRC yielded higher ratings than conventional DRC and linear amplification for overall sound quality and speech clarity at −10 dB SBR. Both DRC strategies resulted in poorer speech clarity ratings than linear amplification at 10 dB SBR. There were no significant differences between the amplification strategies for speech naturalness and music naturalness scales across SBRs. Conclusions: The results are a proof-of-concept that, under ideal circumstances, independent compression of sound sources can improve speech clarity and overall sound quality, particularly when the speech is softer than background music. Generally, DRC may result in poorer speech clarity compared to linear amplification when speech is more intense than background music. The results provide a baseline for future work involving independent compression of sound sources. Supplemental Material: https://doi.org/10.23641/asha.31855201