Comparing classical music interpretations

I built an audio player to easily compare multiple interpretations of the same piece. Here’s an interactive demo, and a video to give you a sense of how it works:


What does it mean to interpret classical music?

At first glance, sheet music is prescriptive: the composer has provided all of the notes, the dynamics (forte, piano), tempo (lento, presto) and changes in tempo (de/accelerando).

In practice, however, the interpreter has a lot of leeway. In some extreme cases, such as the Cadenza in solo concertos, the performer gets to improvize a melody based on a chord progression. Some pieces include ornamentation (eg. trills, etc) which are largely left up to the performer to interpret.

That said, cadenzas and ornaments are somewhat rare. In general, every piece is under-specified by the composer. This gives the performer a lot of leeway to express themselves through the performance, selecting tempo, phrasing, articulation and tone.

Example: Bach’s Goldberg Variations

The Goldberg Variations were composed by Johann Sebastian Bach in 1741, and then popularized by Glenn Gould in his debut album in 1955, transforming a work once considered esoteric into one of the most iconic piano recordings.

In 1981, a year before his death, Gould recorded the pieces again. After a long period of reclusion, he was able to revisit the variations and produce a completely different take. In an interview, he said:

…since I stopped playing concerts, about 20 years, having not played it in all that time, maybe I wasn’t savaged by any over-exposure to it…

Compare Gould’s 1955 and 1981 recordings

Both the 1955 and 1981 recordings are available on YouTube, of course. I found that listening to two distinct performances is not the same as having one integrated player. So I built one: a player specifically for comparing multiple interpretations of the same piece.

Here is a demo that lets you compare the first variation from the Goldberg Variations. Try it out here. You can use your keyboard to skip between interpretations (↑, ↓) just as easily as you can seek within a track (←, →). The mouse works as well. Note that I haven’t tested at all on mobile. Sorry, it’s just a prototype and I’m on paternity leave 😇

I also tried it on Mozart’s Requiem

I am a huge fan of Mozart’s Requiem, and once came across an online thread debating which conductor’s performance was the best. I soon found myself listening to a dozen or so different versions of the same piece. When I was a younger music appreciator, I would often wonder what the point of a conductor really was. I no longer have this question.

Just to give you a taste for how different the interpretations are, here’s an example of three conductors performing the Introitus, the first movement in the Requiem. Check it out here, but be patient as it may take a minute to load and decode the audio. Böhm’s brooding tempo and lumbering chorus (ugh) contrasts especially well with Levin’s crisp and minimalist take.


Technical details

For this prototype, I focused on creating a reasonable UI to play back and interact with multiple time-aligned performances of the same piece. An index file specifies metadata for each track, most importantly the URL to the label file and the URL to the audio file. Each label file is a text file with lines in the format START_TIME END_TIME BAR_NUMBER.

To create the label files, I manually annotated the waveform. Even with Audacity’s extremely useful label track feature, it was a lot of manual work to go through the score, and find each bar’s time range in each recording. At the end of the day, I had start and end times for each bar. For times that don’t fall exactly on bar lines, I linearly interpolate between the bar boundaries, which works reasonably well, but is sometimes a bit off. More granular timing references would address this better, but that currently means doing more manual labor. No thanks!

Science, help me automate this, please

An obvious question is how to automate the labor of synchronizing a recording to a score. In general, I think this is an unsolved problem, especially for complex tracks containing hundreds of instruments and varying levels of background noise.

An promising approach that could work for solo piano music might be to use something like Onsets and Frames to extract piano rolls and then apply something like a Dynamic Time Warp (DTW) in piano roll space. A more general approach might be to synthesize each bar into raw audio (from MIDI), and then align recordings to synthesized audio using something like DTW based on a Constant-Q transform (CQT).

My brief and ill-guided attempts to do something like this on real-world examples didn’t yield good enough results. Any ML/DSP experts want to take this on?


This is a post by Boris Smus, originally from Boris’ website, posted to XRDS with permission of the author.

Information superwhichway revisited: XRDS, 24 years ago

Back in September 1994, the ACM took a bold step into the mostly-unknown, and started its first digital-only publication — Crossroads: The ACM Student Magazine. It has changed through the years, including the transition to a dual-format, digital+printed magazine it is today (and which today seems to be the norm). I found it very interesting (and fun!) to take a look at our first issue, trying to peek into the future that was being forecasted for us almost a quarter of a century ago.

Very aptly, this first issue’s main topic is The Internet. Quite a bold step back then! While the Internet had already existed in some form since the late 1960s, and in a form very similar to what we now use (TCP/IP based networking) since 1983, its use was mostly restricted to academia and military research and communications; while Crossroads was aimed at students on Computer Science-related disciplines, a majority of them didn’t even know much about what this network was about if not for specific needs of their tutors.

Crossroads’ first editor, Saveen Reddy, mentions in his editorial: “The theme of this issue is the Internet and computer networking. These represent relatively recent inventions. However, the general public’s knowledge and appreciation for them is even more recent, spurred on by a deluge of coverage by popular media. Unconfined to military or research purposes, the Internet has grown rapidly. Currently experiencing rapid growth for commercial uses, it is becoming a global resource”.

Commercial use of the Internet had only been allowed in 1993, and its growth was truly explosive. While most of current XRDS readers won’t remember what happened in computing by 1994, I have the relative luck to be a latecomer to formal studies in my life; having been a computer enthusiast as a teenager in the early nineties, I can still remember a world before the Internet.

In its early days, media would usually refer to the Internet as The Information Superhighway — We would laugh at the moniker. And, of course, so did Purdue student Craig Pfeifer when he wrote his article, “Information Superwhichway?”. Of course, if you look at the specific technologies it mentions, the article is indeed old and dated — USENET newsgroups? Apple Newton? FTP and Gopher? Fax machines? MUDs (Multi User Dungeons)? Telnet? Please!

But a slightly deeper reading… Shows in a way the full circle we have described when we talk about humans communicating. It would be foolish of me to argue whether the Internet has changed the way we perceive the world. Reading Pfeifer’s text, his analysis can be almost completely detached from the conjunctural.

Other defining items in communications history

Every technology that has become a basis of strongly improving human ability to communicate has been attacked by the holders of central power. The Gutenberg movable type printing press was a true revolution regarding the spread of culture, but was met with the attempts to control and censor its products via royalty-granted printing licenses (which evolved into what we now know as copyright), as well as the always present church censorship. Nevertheless, with the social effects it had, the printing press is often regarded as the most important invention in history.

Mimeographs were invented in the late 19th century. They didn’t provide a qualitative improvement over the –by then– many available printing processes, but it democratized printing: Mimeographs are portable and cheap, and schools, churches and clubs started printing their own leaflets. But, of course, it meant they could completely escape compulsory censorship regimes. In fact, several revolutions in the early 20th century were strongly fueled by clandestine mimeographers, and trying to stop them became routine (of course, failed routine) for the ruling regimes.

In the eighties and nineties, the very peculiar BBS culture grew with computer enthusiasts around the world. BBSs (Bulletin Board Systems) were mainly hobbyist-run computers with a modem, which usually offered some discussion forums, online games (turn-based, of course, as they had no network connection in the sense we understand it today), and some file sharing; BBSs were the breeding ground for the early free software and shareware distribution models.

Communication was fully decentralized (dozens to hundreds of BBSs existed on most mid-sized cities), near-instantaneous and virtually impossible to control. And, of course, as you can see on the particularly relevant editorial of the April 1993 Boardwatch Magazine, the censorship machinery was quite ready and well oiled throughout the United States. What were the arguments? Alleged distribution of hacking tools and information, software piracy and pornography. Due to the inner cohesion of the BBS community and the noise generated, most of the accused operators were freed after long processes with no charges filed.

The Internet, then and now

Just 18 months after the Boardwatch editorial, Pfeifer’s article in Crossroads talks about the image problems the early commercially available Internet had: “When the Internet is the focus of a story, it’s usually negative. Whether it is how child pornography runs rampant on the Information Superhighway or how easy it is to receive pirated software, it seems that the media doesn’t focus on the positive events that take place daily on the Internet”.

Pfeifer continues, “The Internet never sleeps. It’s kind of like New York, but a little bit cleaner, and the high crime rate isn’t so obvious. Of course, with the influx of new users onto the eighth wonder of the world, there is bound to be some friction. Computer crime will probably increase. The Internet (…) is a system based on trust. But when fiendishly minded people see the Internet as an untapped resource, ripe for the plucking, we have a problem.”

These last paragraphs could perfectly apply today — Only not for the Internet as a whole (it is too much engrained into our social conscience and lifestyle). But this is precisely the kind of attacks we see when talking about privacy-enhancing technologies that try to protect user’s privacy and anonymity on the Internet. Tools akin to what we discussed in the XRDS Summer 2018 issue, which I was honored to be the lead editor for.

And yes, what is the media narrative today when tools such as Tor are discussed? “Oh, but that’s just a gateway to the dark net, and… You don’t want to go there! That’s bad and dangerous. There are loose criminals! There is child porn and drugs, and guns and whatnot!” — Of course, this same narrative was applied to the Internet as a whole back in 1994. Or to the BBSs slightly before that. Or, with scarecrows fit to the spirit of their day, to the agents of social change a hundred or more years ago.

Throughout history, communications technology have appeared that allow for easier, better knowledge circulation. Tools that bring the information flow closer to the individual and further away from the power centers — With that, implying greater surveillance resistance and the ability to remain anonymous. 24 years ago, our magazine started by looking at the great potential Internet held for changing society, although nobody could really forsee the depth of the impact. My hopes are that, over time, privacy enhancement technologies gradually become as engrained into our communication uses as Internet has.

Pfeifer concludes by quoting a then-new meme: “You never know to whom you are writing, because, on the Internet, nobody knows you’re a dog. Somehow, though, and no matter how careful I am, all of the ads I have seen today are for dog food.

ACM SIGAI Launches its 2018 Student Essay Contest…Apply Now!

It’s fall in the States and that means it’s time for the 2018 ACM SIGAI Student Essay Contest on Artificial Intelligence Technologies! Win one of several $500 monetary prizes or a Skype conversation with a leading AI researcher including Joanna Bryson, Murray Campbell, Eric Horvitz, Peter Norvig, Iyad Rahwan, Francesca Rossi, or Toby Walsh.

(The following text is from the ACMSIGAI blog “AI Matters“)

The Contest

The ACM Special Interest Group on Artificial Intelligence (ACM SIGAI) supports the development and responsible application of Artificial Intelligence (AI) technologies. From intelligent assistants to self-driving cars, an increasing number of AI technologies now (or soon will) affect our lives. Examples include Google Duplex (Link) talking to humans, (Link) offering rides in US cities, chatbots advertising movies by impersonating people (Link), and AI systems making decisions about parole (Link) and foster care (Link). We interact with AI systems, whether we know it or not, every day.

Such interactions raise important questions. ACM SIGAI is in a unique position to shape the conversation around these and related issues and is thus interested in obtaining input from students worldwide to help shape the debate. We therefore invite all students to enter an essay in the 2018 ACM SIGAI Student Essay Contest, to be published in the ACM SIGAI newsletter “AI Matters,” addressing one or both of the following topic areas (or any other question in this space that you feel is important) while providing supporting evidence:

  • What requirements, if any, should be imposed on AI systems and technology when interacting with humans who may or may not know that they are interacting with a machine?  For example, should they be required to disclose their identities? If so, how? See, for example, “Turing’s Red Flag” in CACM (Link).
  • What requirements, if any, should be imposed on AI systems and technology when making decisions that directly affect humans? For example, should they be required to make transparent decisions? If so, how?  See, for example, the IEEE’s summary discussion of Ethically Aligned Design (Link).

Each of the above topic areas raises further questions, including

  • Who is responsible for the training and maintenance of AI systems? See, for example, Google’s (Link), Microsoft’s (Link), and IBM’s (Link) AI Principles.
  • How do we educate ourselves and others about these issues and possible solutions? See, for example, new ways of teaching AI ethics (Link).
  • How do we handle the fact that different cultures see these problems differently?  See, for example, Joi Ito’s discussion in Wired (Link).
  • Which steps can governments, industries, or organizations (including ACM SIGAI) take to address these issues?  See, for example, the goals and outlines of the Partnership on AI (Link).

All sources must be cited. However, we are not interested in summaries of the opinions of others. Rather, we are interested in the informed opinions of the authors. Writing an essay on this topic requires some background knowledge. Possible starting points for acquiring such background knowledge are:

  • the revised ACM Code of Ethics (Link), especially Section 3.7, and a discussion of why the revision was necessary (Link),
  • IEEE’s Ethically Aligned Design (Link), and
  • the One Hundred Year Study on AI and Life in 2030 (Link).


ACM brings together computing educators, researchers, and professionals to inspire dialogue, share resources, and address the field’s challenges. As the world’s largest computing society, ACM strengthens the profession’s collective voice through strong leadership, promotion of the highest standards, and recognition of technical excellence. ACM’s reach extends to every part of the globe, with more than half of its 100,000 members residing outside the U.S.  Its growing membership has led to Councils in Europe, India, and China, fostering networking opportunities that strengthen ties within and across countries and technical communities. Their actions enhance ACM’s ability to raise awareness of computing’s important technical, educational, and social issues around the world. See for more information.

ACM SIGAI brings together academic and industrial researchers, practitioners, software developers, end users, and students who are interested in AI. It promotes and supports the growth and application of AI principles and techniques throughout computing, sponsors or co-sponsors AI-related conferences, organizes the Career Network and Conference for early-stage AI researchers, sponsors recognized AI awards, supports AI journals, provides scholarships to its student members to attend conferences, and promotes AI education and publications through various forums and the ACM digital library. See for more information.

Format and Eligibility

The ACM SIGAI Student Essay Contest is open to all ACM SIGAI student members at the time of submission.  (If you are a student but not an ACM SIGAI member, you can join ACM SIGAI before submission for just US$ 11 at by selecting Option 1, even if you are not an ACM member.) Essays can be authored by one or more ACM SIGAI student members but each ACM SIGAI student member can (co-)author only one essay.

All authors must be SIGAI members at the time of submission.  All submissions not meeting this requirement will not be reviewed.

Essays should be submitted as pdf documents of any style with at most 5,000 words via email to

The deadline for submissions is January 10th, 2019.

The authors certify with their submissions that they have followed the ACM publication policies on “Author Representations,” “Plagiarism” and “Criteria for Authorship” ( They also certify with their submissions that they will transfer the copyright of winning essays to ACM.

Judges and Judging Criteria

Winning entries from last year’s essay contest can be found in recent issues of the ACM SIGAI newsletter “AI Matters,” specifically  Volume 3, Issue 3: and  Volume 3, Issue 4:

Entries will be judged by the following panel of leading AI researchers and ACM SIGAI officers. Winning essays will be selected based on depth of insight, creativity, technical merit, and novelty of argument. All decisions by the judges are final.

  • Rediet Abebe, Cornell University
  • Emanuelle Burton, University of Illinois at Chicago
  • Sanmay Das, Washington University in St. Louis
  • John P. Dickerson, University of Maryland
  • Virginia Dignum, Delft University of Technology
  • Tina Eliassi-Rad, Northeastern University
  • Judy Goldsmith, University of Kentucky
  • Amy Greenwald, Brown University
  • H. V. Jagadish, University of Michigan
  • Sven Koenig, University of Southern California
  • Benjamin Kuipers, University of Michigan
  • Nicholas Mattei, IBM Research
  • Alexandra Olteanu, Microsoft Research
  • Rosemary Paradis, Leidos
  • Kush Varshney, IBM Research
  • Roman Yampolskiy, University of Louisville
  • Yair Zick, National University of Singapore


All winning essays will be published in the ACM SIGAI newsletter “AI Matters.” ACM SIGAI provides five monetary awards of USD 500 each as well as 45-minute skype sessions with the following AI researchers:

  • Joanna Bryson, Reader (Assoc. Prof) in AI, University of Bath
  • Murray Campbell, Senior Manager, IBM Research AI
  • Eric Horvitz, Managing Director, Microsoft Research
  • Peter Norvig, Director of Research, Google
  • Iyad Rahwan, Associate Professor, MIT Media Lab and Head of Scalable Corp.
  • Francesca Rossi, AI and Ethics Global Lead, IBM Research AI
  • Toby Walsh, Scientia Professor of Artificial Intelligence, UNSW Sydney, Data61 and TU Berlin

One award is given per winning essay. Authors or teams of authors of winning essays will pick (in a pre-selected order) an available Skype session or one of the monetary awards until all Skype sessions and monetary awards have been claimed. ACM SIGAI reserves the right to substitute a Skype session with a different AI researcher or a monetary award for a Skype session in case an AI researcher becomes unexpectedly unavailable. Some prizes might not be awarded in case the number of high-quality submissions is smaller than the number of prizes.


In case of questions, please first check the ACM SIGAI blog for announcements and clarifications: You can also contact the ACM SIGAI Student Essay Contest Organizers at

  • Nicholas Mattei (IBM Research) – ACM SIGAI Student Essay Contest Organizer and AI and Society Officer

with involvement from

  • Sven Koenig (University of Southern California), ACM SIGAI Chair
  • Sanmay Das (Washington University in St. Louis), ACM SIGAI Vice Chair
  • Rosemary Paradis (Leidos), ACM SIGAI Secretary/Treasurer
  • Benjamin Kuipers (University of Michigan), ACM SIGAI Ethics Officer
  • Amy McGovern (University of Oklahoma), ACM SIGAI AI Matters Editor-in Chief


The World’s Most Active ACM Student Chapters Video Series

Episode 2: Cornell University ACM-W Student Chapter, USA

The representation of women and other underrepresented groups in STEM (Science, Technology, Engineering, and Medicine) fields has been a much debated topic throughout the tech industry and academia in recent times. With so much attention and effort made to improve representation within industry, student-led bodies are doing their part, if not more. One of these student organizations is WICC (Women In Computing At Cornell), whose core mission is to empower women to carve their own paths in the field of computer science.

WICC is one of the most recognized ACM-W Chapters in North America, and it works tirelessly toward its mission. Alongside some great individuals from their team,  over the past few months XRDS worked with WICC to find the best way to showcase their hardwork. Just as we featured the UPES ACM Student Chapter in our first video, we bring to you our second episode in the series, featuring the ACM-W chapter from Cornell University: WICC.

We hope you’ll enjoy seeing the video as much as we enjoyed making it! And please do visit their social media channels to learn more about them.

Foolproof Formulas for Boosting Your Academic Social Media

Featured image for blog post by Cori Faklaris: More of What Works in Social Media (For Academics)

The second of 2 blog posts on tips for academics to use social media to reach a wider audience for their research and for their careers.

Use principles such as consistency, reciprocity and the 2:1 rule to build up your content and followers on your professional social media accounts.

So you’ve set up your social media accounts on Twitter, Facebook and LinkedIn. (Didn’t do that yet? See my first post: “A Professional Academic’s Guide to Using Social Media.”) Now what?

Below, I provide a few of my “tricks of the trade” — lessons I’ve learned in my time managing my own online brand and those of my employers and clients on social media. These ideas will help social media enthusiasts to go about systematically building their content and followers the way the non-academic pros do it.

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