Section: New Results
Towards comprehensive audio scene analysis
Source localization and separation, machine learning, room geometry, room properties, multichannel audio classification
By contrast to the previous lines of work and results on source localization and separation, which are mostly focused on the sources, the following emerging activities consider the audio scene and its analysis in a wider sense, including the environment around the sources, and in particular the room they are included in, and their properties. This inclusive vision of the audio scene allows in return to revisit classical audio processing tasks, such as localization, separation or classification.
Room Properties: Estimating or Learning Early Echoes
Participants : Nancy Bertin, Diego Di Carlo, Clément Elvira.
Main collaborations: Antoine Deleforge (Inria Nancy – Grand Est), Ivan Dokmanic (University of Illinois at Urbana-Champaign, Coordinated Science Lab, USA), Robin Scheibler (Tokyo Metropolitan University, Tokyo, Japan), Helena Peic-Tukuljac (EPFL, Switzerland).
In  we showed that the knowledge of early echoes improved sound source separation performances, which motivates the development of (blind) echo estimation techniques. Echoes are also known to potentially be a key to the room geometry problem . In 2019, two different approaches to this problem were explored.
As a competitive, yet similar approach to our previous work in , we proposed a new analytical method for off-the-grid early echoes estimation, based on continuous dictionaries and extensions of sparse recovery methods in this setting. From the well-known cross-relation between room impulse responses and signals in a “one source - two microphones” settings, the echo estimation problem can be recast as a Beurling-LASSO problem and solved with algorithms of this kind. This enables near-exact blind and off-grid echo retrieval from discrete-time measurements, and can outperform conventional methods by several orders of magnitude in precision, in an ideal case where the room impulse response is limited to a few weighted Diracs. Future work will include alternative initialization schemes, extensions to sparse-spectrum signals and noisy measurements, and applications to dereverberation and audio-based room shape reconstruction. This work, mostly lead by Clément Elvira, was submitted for publication in Icassp 2020.
On the other hand, the PhD thesis of Diego Di Carlo aims at applying the “Virtual Acoustic Space Traveler” (VAST) framework to the blind estimation of acoustic echoes, or other room properties (such as reverberation time, acoustic properties at the boundaries, etc.) Last year, we focused on identifying promising couples of inputs and outputs for such an approach, especially by leveraging the notions of relative transfer functions between microphones, the room impulse responses, the time-difference-of-arrivals, the angular spectra, and all their mutual relationships. In a simple yet common scenario of 2 microphones close to a reflective surface and one source (which may occur, for instance, when the sensors are placed on a table such as in voice-based assistant devices), we introduced the concept of microphone array augmentation with echoes (MIRAGE) and showed how estimation of early-echo characteristics with a learning-based approach is not only possible but can in fact benefit source localization. In particular, it allows to retrieve 2D direction of arrivals from 2 microphones only, an impossible task in anechoic settings. These first results were published in ICASSP . In 2019, we improved the involved DNN architecture in MIRAGE and worked towards experimental validation of this result, by designing and recording a data set with annotated echoes in different conditions of reverberation. Future work will include extension of this data set, extension to more realistic and more complex scenarios (including more microphones, sources and reflective surfaces) and the estimation of other room properties such as the acoustic absorption at the boundaries, or ultimately, the room geometry. Some of these tracks currently benefit from the visit of Diego di Carlo to Bar-Ilan University (thanks to a MathSTIC doctoral outgoing mobility grant.)
Multichannel Audio Event and Room Classification
Participants : Marie-Anne Lacroix, Nancy Bertin.
Main collaborations: Pascal Scalart, Romuald Rocher (GRANIT Inria project-team, Lannion)
Typically, audio event detection and classification is tackled as a “pure” single-channel signal processing task. By constrast, audio source localization is the perfect example of multi-channel task “by construction”. In parallel, the need to classify the type of scene or room has emerged, in particular from the rapid development of wearables, the “Internet of things” and their applications. The PhD of Marie-Anne Lacroix, started in September 2018, combines these ideas with the aim of developing multi-channel, room-aware or spatially-aware audio classification algorithms for embedded devices. The PhD topic includes low-complexity and low-energy stakes, which will be more specifically tackled thanks to the GRANIT members area of expertise. During the first year of the PhD, we gathered existing data and identified the need for new simulations or recordings, and combined ideas from existing single-channel classification techniques with traditional spatial features in order to design several baseline algorithms for multi-channel joint localization and classification of audio events. The impact of feature quantization on classification performance is also currently under investigation and a participation to the 2020 edition of the IEEE AASP Challenge on Detection and Classification of Acoustic Scenes and Events (DCASE) is envisioned.