directtoreverberant

Direct-to-reverberant ratio (DRR) is a metric used in room acoustics and audio signal processing to quantify the balance between direct sound from a source and the late reverberant field reaching a listener. It is typically expressed in decibels as DRR = 10 log10(E_direct / E_reverberant). The direct component corresponds to sound that travels along a direct path and arrives shortly after emission, while the reverberant component consists of energy from reflections off room surfaces that arrives later.

Measurement and estimation usually rely on impulse responses or controlled stimuli. After a measured or simulated impulse response is obtained, energy is separated into an early direct portion (a short time window after onset) and a late reverberant portion. The ratio of these energies yields the DRR, which can be computed for the full bandwidth or for specific frequency bands to yield a frequency-dependent DRR.

DRR is a key parameter in evaluating room acoustics, speech intelligibility, and the design of microphones, loudspeakers, and hearing aids. It also informs dereverberation and source separation algorithms, where higher DRR typically indicates clearer direct sound relative to reflections. Values vary with source–listener distance, room size and absorption, speaker orientation, and frequency content; larger or more reverberant spaces tend to produce lower DRR at a given location, particularly at higher frequencies.

In practice, DRR complements measures such as RT60 and STI (speech transmission index) in characterizing acoustic environments and predicting perceptual speech clarity.