The reproduction of speech over loudspeakers in a reverberant environment is often encountered in daily life, as for example, in a train station or during a telephone conference. Spatial reverberation degrades intelligibility. This study proposes two perceptually motivated preprocessing approaches that are applied to the dry speech before being played into a reverberant environment. In the first algorithm, which assumes prior knowledge of the room impulse response, the amount of...

The ability to localize sound sources in reverberant environments is dependent upon first-arriving information, an outcome commonly termed “the precedence effect.” For example, in laboratory experiments, the combination of a leading (direct) sound followed by a lagging (reflected) sound is localized in the direction of the leading sound. This study was designed to measure the degree to which stimulus compactness/diffuseness (i.e., coherence as represented by interaural cross correlation) of leading and lagging sounds influences performance. The compactness/diffuseness of leading or lagging sounds was varied by either presenting a sound from a single loudspeaker or by presenting mutually uncorrelated versions of similar sounds from nine adjacent loudspeakers. In separate experiments, the listener's task was to point to the perceived location of leading and lagging 10-ms long low-pass filtered white noises or 2-s long tokens of speech. The leading and lagging stimuli were presented either from speakers located directly in front of the listeners or from speakers located ±45° to the right or left. The results indicate that leading compact (coherent) sounds influence perceived location more so than do leading diffuse (incoherent) sounds. This was true independent of whether the sounds were Gaussian noises or tokens of speech.

State-of-the-art stereo recording techniques using two microphones have two main disadvantages: first, a limited reduction of the reverberation in the direct sound component, and second, compression or expansion of the angular position of sound sources. To address these disadvantages, the aim of this study is the development of a true stereo recording microphone array that aims to record the direct and reverberant sound field separately. This array can be used within the recording and playback configuration developed in Grosse and van de Par, 2015. Instead of using only two microphones, the proposed method combines two logarithmically-spaced microphone arrays, whose directivity patterns are optimized with a superdirective beamforming algorithm. The optimization allows us to have a better control of the overall beam pattern and of interchannel level differences. A comparison between the newly-proposed system and existing microphone techniques shows a lower percentage of the recorded reverberance within the sound field.

In daily life, we are often exposed to speech that is rendered over loudspeakers in a reverberant acoustical environment (examples are public-address systems used in a train station or conference halls). Whereas the early reflections can support speech intelligibility, the late reflections smear the speech in time which will result in an overlap of consecutive speech portions and an effective low-pass filtering of the speech-specific modulation spectrum. This study proposes a perceptually motivated pre-processing approach, based on previous work of Hodoshima et al. [J. Acoust. Soc. 119, 4055-4064 (2006)], which reduces the detrimental effects of reverberation by suppressing steady-state portions and emphasizing potentially inaudible/masked segments of speech before it is emitted in the reverberant environment. For pre-processing, the impulse response is separated into a direct and a reverberant path to decide whether speech segments are inaudible and can be neglected or should be emphasized. A speech intelligibility prediction model is used to select the optimal pre-processing parameters for each specific acoustical environment. Listening tests showed, that this pre-processing approach is able to partially compensate the detrimental effects of reverberation leading to a reduction in speech reception thresholds of about 2 to 5 dB measured in speech shaped noise.

The ability to localize sound sources in reverberant environments is dependent upon first-arriving information, an outcome commonly termed “the precedence effect.” For example, a combination of a leading (direct) sound followed by a lagging (reflected) sound is localized in the direction of the leading sound. We measured how the compactness/diffuseness (i.e., the interaural coherence) of leading and lagging sounds, respectively, influences performance. The compactness/diffuseness of leading or lagging sounds was varied by either presenting a sound from a single loudspeaker or by presenting mutually uncorrelated versions of similar sounds from nine adjacent loudspeakers. The listener pointed to the perceived location of leading and lagging sources of sounds which were 10-ms long, low-pass filtered white noises or 2-second long tokens of speech. The sounds were presented either from speakers located directly in front of the listener or from speakers located 45° to the right or left. Leading compact/coherent sounds, be they Gaussian noises or tokens of speech, influenced perceived location more so than did leading diffuse/incoherent sounds. The results strongly support the hypothesis that stimulus coherence, often modeled by “straightness” within a cross-correlogram, plays an important role in precedence.