Sound Quality & Design

Mp3 compression is commonly used to reduce the size of digital music files but introduces a number of potentially audible artifacts, especially at low bitrates. We investigated whether listeners prefer CD quality to mp3 files at various bitrates (96 kb/s to 320 kb/s), and whether this preference is affected by musical genre. Thirteen trained listeners completed an A/B comparison task judging CD quality and compressed files. Listeners significantly preferred CD quality to mp3 files up to 192 kb/s for all musical genres. In addition, we observed a significant effect of expertise (sound engineers vs. musicians) and musical genres (electric v.s acoustic music).

It is currently common practice for sound engineers to record digital music using high-resolution formats, and then down sample the files to 44.1kHz for commercial release. This study aims at investigating whether listeners can perceive differences between musical files recorded at 44.1kHz and 88.2kHz with the same analog chain and type of AD-converter. Sixteen expert listeners were asked to compare 3 versions (44.1kHz, 88.2kHz and the 88.2kHz version down-sampled to 44.1kHz) of 5 musical excerpts in a blind ABX task. Overall, participants were able to discriminate between files recorded at 88.2kHz and their 44.1kHz down-sampled version. Furthermore, for the orchestral excerpt, they were able to discriminate between files recorded at 88.2kHz and files recorded at 44.1kHz.

The article outlines a psychoacoustically founded method to describe the acoustic performance of earphones in two dimensions, Spectral Shape and Stereo Image Coherence. In a test set of 14 typical earphones, these dimensions explained 66.2% of total variability in 11 acoustic features based on Bark band energy distribution. We designed an interactive Earphone Simulator software that allows smooth interpolation between measured earphones, and employed it in a controlled experiment (N=30). Results showed that the preferred ‘virtual earphone’ sound was different between two test conditions, silence and commuter noise, both in terms of gain level and spectral shape. We discuss possible development of the simulator design for use in perceptual research as well as in commercial applications.

The amount of available audio data is increasing rapidly in consequence of advancements in media creation, storage and
compression technologies. This rapid increase imposes new demands in audio data management and retrieval.
In this work, we proposed an audio data model and repository model to fulfill user requirements in retrieving audio data from large collections. The proposed audio data repository model facilitates a multi-criteria query formulation and audio data retrieval where by audio can be queried both by its low- and high-level features. In the proposed model, a generic audio repository model that can handle a general audio as well as a sub-repository model that can manipulate speech through its constituent units is discussed. Finally, the viability of the proposed model is demonstrated by a prototype system
developed for an application in the medical domain.

Keywords: Audio data model, audio data repository model, Multi-criteria audio data retrieval, Audio Data Management for Medical Application (ADMMA).

An experiment has been carried out on the perceived quality of a specific category of mechanical
devices – the turbo molecular vacuum pumps used in industries and laboratories – from their noise emitted
during the full speed functioning and the warming up phase. The test fits with a real problem of
constructors that often need to manage complaints from customers returning perfectly working pumps as
their sound generates a malfunction feeling. On the total number of participants (81 subjects), two groups
have been selected – expert listeners and naïve – and submitted to two tests: open questionnaire during a
jury test and pairs comparison. The parameters investigated through different methods have been mainly:
the annoyance, the general preference and the impression of proper operation. Data analysis considers both
the influence of different investigation methodologies and the correlation with classical parameters of
psychoacoustics. Different models of turbo molecular vacuum pumps have been the objects of the study
and a full acoustic characterization of these sources has been done.