Belgium on Sunday broke its own standing record for the longest political crisis and longest period without an elected government. It has been 592 days since the previous government, led by former Prime Minister Charles Michel, collapsed over inter-party tensions on migration in December 2018. Strained negotiations after last year’s elections in May have routinely collapsed as party leaders and several top government officials resign from their mission to steer the coalition negotiations. The previous record for Belgium’s longest post-election period without a government stands at 541 days and ended with the swearing-in of Former Prime Minister Elio Di Rupo after a similarly convoluted negotiation period followed the June 2010 elections.
Many ideas were based on a paper by Yan Ke, Derek Hoiem, and Rahul Sukthankar called “Computer Vision for Music Identification” (2005). In fact, even the Last.fm fingerprinter uses the code published by the authors of this paper. This is where I learned that audio identification is more about machine learning that it is about DSP. Many useful methods for extracting interesting features from audio streams are well-known and the problem is more about how to apply and index them the best way. The basic idea here is to treat audio as a spectral image and index the content of the image. I’ll explain this in more detail and how Chromaprint uses this in a following post. Another important paper for me was “Pairwise Boosted Audio Fingerprint” (2009) by Dalwon Jang, Chang D. Yoo, Sunil Lee, Sungwoong Kim and Ton Kalker (Ton Kalker is a co-author of a historically important paper “Robust Audio Hashing for Content Identification” (2001) published by Philips Research), which combined previous experiments of the authors with audio identification based on spectral centroid features and the indexing approach similar to the one suggested by Y. Ke, D. Hoiem and R. Sukthankar. For a long time this was the best solution I had and since it was actually not very hard to implement, the most time I spent on tweaking the configuration to get the best results. The last major change came after I learned about “chroma” features by reading the “Efficient Index-Based Audio Matching” (2008) by Frank Kurth and Meinard Müller. I’ve read more papers about chroma features later, but this was the first and also the most important one for me and some ideas about processing the feature vectors from it are implemented in Chromaprint. Chroma features are typically used for music identification, as opposed to audio file identification, but I tried to use them with the approach I already had implemented and it nicely improved the quality of the fingerprinting function and actually reduced complexity which allowed me to use much larger training data sets.