Verovio: Fixing MIDI Overlap On Tempo Changes
Hey everyone! Today, we're diving deep into a fascinating problem encountered in Verovio, a powerful music notation engraving library. Specifically, we're tackling an issue where midi measures overlap during tempo changes. This can lead to some pretty funky playback, with notes from different measures bleeding into each other. Let's break down the problem, how to reproduce it, and what we expect to happen.
Understanding the Midi Measures Overlap Issue
The core issue revolves around tempo changes within a musical score. When the tempo shifts, Verovio's midi rendering sometimes gets a little confused, causing the timing of notes to misalign. This results in notes from one measure spilling over into the next, creating an undesirable overlapping effect. Imagine hearing the end of measure 1 clashing with the beginning of measure 2 – not exactly harmonious, right? This overlap in midi playback can be particularly noticeable in pieces with frequent or drastic tempo changes.
To fully grasp the problem, it’s essential to understand how Verovio handles tempo information. Tempo markings in a musical score dictate the speed at which the music is played. These markings are typically expressed in beats per minute (BPM) and can change throughout a piece. Verovio interprets these tempo changes and adjusts the timing of midi notes accordingly. However, in certain cases, the calculations or the synchronization between the visual rendering and the midi playback might falter, leading to the midi overlap we're discussing. The complexity arises from the need to accurately translate musical time, which is often expressed in relative terms (like quarter notes or eighth notes), into absolute time (like seconds or milliseconds) for midi playback. This translation becomes tricky when tempo changes introduce variations in the duration of these relative time units. For example, a quarter note at 120 BPM will have a different duration than a quarter note at 180 BPM, and ensuring that these durations are correctly reflected in the midi output is crucial for accurate playback.
Furthermore, the issue might be influenced by the specific way tempo changes are encoded in the MusicXML file. MusicXML, being a flexible format, allows for different ways of representing tempo markings. Some encodings might be more prone to this overlap issue than others. It's also possible that the way Verovio parses and interprets these different encodings plays a role in the problem. Therefore, a thorough understanding of both MusicXML's tempo representation and Verovio's parsing logic is necessary to pinpoint the exact cause of the bug. In addition to the encoding itself, the placement of tempo markings within the score can also impact the midi playback. If tempo changes are placed at unusual or ambiguous locations, Verovio might misinterpret the intended timing. For instance, a tempo change placed in the middle of a measure, rather than at the beginning, might lead to unexpected behavior. Therefore, analyzing the specific placement of tempo markings in the problematic XML file is an important step in diagnosing the issue. The challenge is to ensure that the midi playback accurately reflects the composer's intended timing, even when the score contains complex tempo variations and potentially ambiguous notation. This requires a robust and precise mechanism for translating musical time into midi time, taking into account all the nuances of tempo changes and their representation in the score.
Reproducing the Issue: A Step-by-Step Guide
So, how can you see this midi overlap in action? It's actually quite straightforward. Here’s a step-by-step guide to reproduce the problem:
- Load the data: First, you'll need the problematic MusicXML data. You can find the XML code snippet provided in the original post (see below). Copy this code.
- Open editor.verovio.org: Head over to editor.verovio.org in your web browser. This is Verovio's online editor, a handy tool for testing and debugging.
- Paste the XML: Paste the copied MusicXML code into the editor. This will load the musical score into Verovio.
- Hit Play: Now, the moment of truth! Click the play button in the editor to start midi playback.
If the issue is present, you should clearly hear the midi overlap, particularly at the transition between measures 1 and 2. The sounds from these measures will blend together in a way that doesn't align with the intended musical rhythm. This simple test allows anyone to quickly verify the bug and understand its impact on the listening experience. It's a crucial step in the debugging process, as it provides a concrete example of the problem that developers can then investigate and fix. The ease of reproduction also means that users can easily report the issue and provide a clear demonstration of the bug, which helps developers prioritize and address it effectively. Moreover, reproducing the issue in different environments (e.g., different browsers, operating systems, or Verovio versions) can help identify the root cause of the problem. If the midi overlap only occurs in certain environments, it suggests that the bug might be related to platform-specific factors or interactions with other software components. Therefore, thorough testing across various platforms is essential for ensuring that the fix is robust and addresses the issue for all users.
Expected Behavior: Clean and Distinct Measures
Now, let’s talk about what should happen. The expected behavior is that the midi output from each measure should be distinct and clear. There should be no overlapping sounds or notes bleeding from one measure into another. When measure 1 finishes, the sound should cleanly transition to measure 2, and so on. This ensures that the musical rhythm and timing are accurately represented in the midi playback. The tempo changes should be smooth and seamless, without any audible glitches or artifacts. In essence, the midi output should mirror the visual notation, providing an accurate and faithful representation of the musical score.
Achieving this expected behavior is crucial for several reasons. First and foremost, it ensures that the music sounds correct and as intended by the composer. Overlapping notes or misplaced rhythms can significantly distort the musical expression and make the piece sound disjointed or even incorrect. Secondly, accurate midi playback is essential for music education and analysis. Students and musicians rely on midi output to hear and understand the nuances of musical scores, and any inaccuracies in the playback can hinder their learning and comprehension. Thirdly, clean midi output is vital for music production and performance. Midi is a fundamental tool for creating and manipulating music electronically, and accurate timing is paramount for these applications. Therefore, ensuring that Verovio's midi rendering is precise and free from overlaps is a critical step in making it a reliable and versatile tool for musicians and developers alike. The challenge lies in accurately translating the musical notation into midi events, taking into account all the complexities of tempo changes, time signatures, and other musical elements. This requires a sophisticated algorithm that can correctly interpret the score and generate midi output that faithfully reflects the composer's intentions. The goal is to create a seamless and intuitive experience for users, where the midi playback sounds exactly as they expect it to, regardless of the complexity of the score.
The XML Input Data
For those who want to dive into the code, here’s the XML data that triggers the issue:
<?xml version="1.0" ?>
<score-partwise version="4.0">
<work>
<work-title>C Major</work-title>
</work>
<identification>
<encoding>
<encoding-date>2025-08-10</encoding-date>
<software/>
</encoding>
<miscellaneous>
<miscellaneous-field name="rhythm">Reel</miscellaneous-field>
</miscellaneous>
</identification>
<defaults>
<scaling>
<millimeters>7</millimeters>
<tenths>40</tenths>
</scaling>
</defaults>
<part-list>
<score-part id="P1">
<part-name/>
</score-part>
</part-list>
<!--=========================== Part 1 ===========================-->
<part id="P1">
<!--========================= Measure 1 ==========================-->
<measure number="1" implicit="no">
<attributes>
<divisions>10080</divisions>
<key>
<fifths>0</fifths>
<mode>major</mode>
</key>
<time>
<beats>4</beats>
<beat-type>4</beat-type>
</time>
</attributes>
<direction placement="above">
<direction-type>
<metronome parentheses="no">
<beat-unit>quarter</beat-unit>
<per-minute>120</per-minute>
</metronome>
</direction-type>
<sound tempo="120"/>
</direction>
<note>
<pitch>
<step>C</step>
<octave>4</octave>
</pitch>
<duration>5040</duration>
<type>eighth</type>
<beam number="1">begin</beam>
</note>
<note>
<pitch>
<step>D</step>
<octave>4</octave>
</pitch>
<duration>5040</duration>
<type>eighth</type>
<beam number="1">continue</beam>
</note>
<note>
<pitch>
<step>E</step>
<octave>4</octave>
</pitch>
<duration>5040</duration>
<type>eighth</type>
<beam number="1">continue</beam>
</note>
<note>
<pitch>
<step>F</step>
<octave>4</octave>
</pitch>
<duration>5040</duration>
<type>eighth</type>
<beam number="1">continue</beam>
</note>
<note>
<pitch>
<step>G</step>
<octave>4</octave>
</pitch>
<duration>5040</duration>
<type>eighth</type>
<beam number="1">continue</beam>
</note>
<note>
<pitch>
<step>A</step>
<octave>4</octave>
</pitch>
<duration>5040</duration>
<type>eighth</type>
<beam number="1">continue</beam>
</note>
<note>
<pitch>
<step>B</step>
<octave>4</octave>
</pitch>
<duration>5040</duration>
<type>eighth</type>
<beam number="1">continue</beam>
</note>
<note>
<pitch>
<step>C</step>
<octave>5</octave>
</pitch>
<duration>5040</duration>
<type>eighth</type>
<beam number="1">end</beam>
</note>
</measure>
<!--========================= Measure 2 ==========================-->
<measure number="2" implicit="no">
<direction placement="above">
<direction-type>
<metronome parentheses="no">
<beat-unit>quarter</beat-unit>
<per-minute>180</per-minute>
</metronome>
</direction-type>
<sound tempo="180"/>
</direction>
<note>
<pitch>
<step>C</step>
<octave>4</octave>
</pitch>
<duration>5040</duration>
<type>eighth</type>
<beam number="1">begin</beam>
</note>
<note>
<pitch>
<step>D</step>
<octave>4</octave>
</pitch>
<duration>5040</duration>
<type>eighth</type>
<beam number="1">continue</beam>
</note>
<note>
<pitch>
<step>E</step>
<octave>4</octave>
</pitch>
<duration>5040</duration>
<type>eighth</type>
<beam number="1">continue</beam>
</note>
<note>
<pitch>
<step>F</step>
<octave>4</octave>
</pitch>
<duration>5040</duration>
<type>eighth</type>
<beam number="1">continue</beam>
</note>
<note>
<pitch>
<step>G</step>
<octave>4</octave>
</pitch>
<duration>5040</duration>
<type>eighth</type>
<beam number="1">continue</beam>
</note>
<note>
<pitch>
<step>A</step>
<octave>4</octave>
</pitch>
<duration>5040</duration>
<type>eighth</type>
<beam number="1">continue</beam>
</note>
<note>
<pitch>
<step>B</step>
<octave>4</octave>
</pitch>
<duration>5040</duration>
<type>eighth</type>
<beam number="1">continue</beam>
</note>
<note>
<pitch>
<step>C</step>
<octave>5</octave>
</pitch>
<duration>5040</duration>
<type>eighth</type>
<beam number="1">end</beam>
</note>
</measure>
<!--========================= Measure 3 ==========================-->
<measure number="3" implicit="no">
<direction placement="above">
<direction-type>
<metronome parentheses="no">
<beat-unit>quarter</beat-unit>
<per-minute>90</per-minute>
</metronome>
</direction-type>
<sound tempo="90"/>
</direction>
<note>
<pitch>
<step>C</step>
<octave>4</octave>
</pitch>
<duration>5040</duration>
<type>eighth</type>
<beam number="1">begin</beam>
</note>
<note>
<pitch>
<step>D</step>
<octave>4</octave>
</pitch>
<duration>5040</duration>
<type>eighth</type>
<beam number="1">continue</beam>
</note>
<note>
<pitch>
<step>E</step>
<octave>4</octave>
</pitch>
<duration>5040</duration>
<type>eighth</type>
<beam number="1">continue</beam>
</note>
<note>
<pitch>
<step>F</step>
<octave>4</octave>
</pitch>
<duration>5040</duration>
<type>eighth</type>
<beam number="1">continue</beam>
</note>
<note>
<pitch>
<step>G</step>
<octave>4</octave>
</pitch>
<duration>5040</duration>
<type>eighth</type>
<beam number="1">continue</beam>
</note>
<note>
<pitch>
<step>A</step>
<octave>4</octave>
</pitch>
<duration>5040</duration>
<type>eighth</type>
<beam number="1">continue</beam>
</note>
<note>
<pitch>
<step>B</step>
<octave>4</octave>
</pitch>
<duration>5040</duration>
<type>eighth</type>
<beam number="1">continue</beam>
</note>
<note>
<pitch>
<step>C</step>
<octave>5</octave>
</pitch>
<duration>5040</duration>
<type>eighth</type>
<beam number="1">end</beam>
</note>
</measure>
<!--========================= Measure 4 ==========================-->
<measure number="4" implicit="no">
<direction placement="above">
<direction-type>
<metronome parentheses="no">
<beat-unit>quarter</beat-unit>
<per-minute>120</per-minute>
</metronome>
</direction-type>
<sound tempo="120"/>
</direction>
<note>
<pitch>
<step>C</step>
<octave>4</octave>
</pitch>
<duration>5040</duration>
<type>eighth</type>
<beam number="1">begin</beam>
</note>
<note>
<pitch>
<step>D</step>
<octave>4</octave>
</pitch>
<duration>5040</duration>
<type>eighth</type>
<beam number="1">continue</beam>
</note>
<note>
<pitch>
<step>E</step>
<octave>4</octave>
</pitch>
<duration>5040</duration>
<type>eighth</type>
<beam number="1">continue</beam>
</note>
<note>
<pitch>
<step>F</step>
<octave>4</octave>
</pitch>
<duration>5040</duration>
<type>eighth</type>
<beam number="1">continue</beam>
</note>
<note>
<pitch>
<step>G</step>
<octave>4</octave>
</pitch>
<duration>5040</duration>
<type>eighth</type>
<beam number="1">continue</beam>
</note>
<note>
<pitch>
<step>A</step>
<octave>4</octave>
</pitch>
<duration>5040</duration>
<type>eighth</type>
<beam number="1">continue</beam>
</note>
<note>
<pitch>
<step>B</step>
<octave>4</octave>
</pitch>
<duration>5040</duration>
<type>eighth</type>
<beam number="1">continue</beam>
</note>
<note>
<pitch>
<step>C</step>
<octave>5</octave</n </pitch>
<duration>5040</duration>
<type>eighth</type>
<beam number="1">end</beam>
</note>
</measure>
</part>
</score-partwise>
This XML snippet contains a simple musical score with tempo changes between measures. By examining this code, developers can gain insights into how tempo markings are encoded and how Verovio interprets them. The presence of tempo changes in measures 2 and 3 is a key factor in triggering the midi overlap issue. Analyzing the specific values and placement of these tempo markings can help identify the root cause of the bug. Furthermore, the structure of the XML file itself might play a role in the problem. The way the musical score is organized, the attributes associated with each note, and the overall hierarchy of the XML elements can all influence how Verovio processes the data. Therefore, a comprehensive understanding of the XML structure, in conjunction with the tempo markings, is essential for debugging the issue.
It's also worth noting that the divisions attribute in the <attributes> element specifies the number of time divisions per quarter note. This value is crucial for calculating the duration of notes and rests in the score. If this value is inconsistent or incorrect, it can lead to timing issues in the midi playback. Therefore, verifying the accuracy of the divisions attribute is another important step in diagnosing the midi overlap problem. The goal is to ensure that all the timing-related parameters in the XML file are correctly encoded and consistently interpreted by Verovio, so that the midi output accurately reflects the intended musical timing.
Verovio and Environment Information
This issue was observed on editor.verovio.org and also reproduced locally on Verovio version afc927589f2f0ad6b392cf559a722ca365ccff32 using the JS binding. The environment details are:
- OS: MacOS
- Browser: Chrome
This information is crucial for developers to replicate the issue in a controlled environment. Knowing the specific Verovio version and the operating system and browser used can help narrow down the potential causes of the bug. For example, if the issue only occurs on a particular operating system or browser, it suggests that the bug might be related to platform-specific libraries or APIs. Similarly, if the issue is only present in a specific Verovio version, it indicates that the bug might have been introduced or fixed in that version. Therefore, providing detailed environment information is an essential part of bug reporting and helps developers efficiently identify and resolve the problem.
The fact that the issue was reproduced both on the online editor and locally suggests that the bug is likely in Verovio's core logic, rather than being specific to the online editor environment. This makes it easier for developers to focus their efforts on the relevant part of the codebase. However, it's still important to test the fix in both environments to ensure that it resolves the issue in all contexts. The JS binding information is also relevant, as it indicates that the bug is present in the JavaScript interface of Verovio. This might have implications for how the bug is fixed, as the fix needs to be compatible with the JavaScript environment. The goal is to provide a comprehensive picture of the environment in which the issue occurs, so that developers have all the information they need to effectively debug and resolve the problem.
Conclusion: Fixing the Midi Overlap
The midi measures overlap issue in Verovio, particularly when dealing with tempo changes, is a significant bug that impacts the accuracy of midi playback. By understanding the problem, knowing how to reproduce it, and clearly defining the expected behavior, we can help developers address this issue effectively. The provided XML data and environment information offer a solid foundation for debugging and testing a solution. Let's hope this gets squashed soon so we can all enjoy seamless midi playback in Verovio! This deep dive into the problem not only helps in resolving the specific bug but also enhances our understanding of the complexities involved in music notation and midi rendering. The collaboration between users and developers, through detailed bug reports and clear reproduction steps, is key to making Verovio an even more robust and reliable tool for the music community.
