International Audio Laboratories Erlangen

Pitch Estimation in Real Time: Revisiting SWIPE with Causal Windowing

Peter Meier, Sebastian Strahl, Simon Schwär, Meinard Müller, Stefan Balke

This website is related to the following publication:

1. Peter Meier, Sebastian Strahl, Simon Schwär, Meinard Müller, and Stefan Balke
   Pitch Estimation in Real Time: Revisiting SWIPE With Causal Windowing
   In Proceedings of the International Symposium on Computer Music Multidisciplinary Research (CMMR), 2025, Accepted. Bibtex

   @inproceedings{MeierSSMB25_RealTimeSWIPE_CMMR,
   author    = {Peter Meier and Sebastian Strahl and Simon Schw{\"a}r and Meinard M{\"u}ller and Stefan Balke},
   title     = {Pitch Estimation in Real Time: Revisiting {SWIPE} With Causal Windowing},
   booktitle = {Proceedings of the International Symposium on Computer Music Multidisciplinary Research ({CMMR})},
   address   = {London, UK},
   year      = {2025, Accepted}
   }

Abstract

Pitch estimation in real time is essential for a wide range of Music Information Retrieval (MIR) applications, including intonation monitoring, music education, and interactive systems. Many of these use cases, such as ensemble rehearsal settings, require low-latency, multi-channel processing on resource-constrained devices. While recent neural approaches offer high accuracy, they often fall short in real-time performance due to computational demands. In this paper, we revisit the well-established SWIPE algorithm and introduce RT-SWIPE, a real-time variant enabled by using causal windowing. We further propose a delay-tolerant evaluation metric that extends Raw Pitch Accuracy (RPA) to account for algorithmic delays. Experimental results on synthetic signals and multi-track ensemble recordings demonstrate that RT-SWIPE provides a practical balance of latency, accuracy, and efficiency. Although our study focuses on wind orchestra scenarios, the method is broadly applicable to similar real-time settings.

Application Scenario 1: Intonation Monitoring

The first application scenario for the RT-SWIPE algorithm is a real-time intonation monitoring system [3] designed for music ensembles. This system provides immediate feedback to both musicians and conductors, enabling collaborative rehearsal practices and improved ensemble tuning. By leveraging the RT-SWIPE algorithm, the system achieves low-latency, multi-channel pitch estimation, making it suitable for resource-constrained environments.

The accompanying video demonstrates the system in action, showcasing how individual musicians receive personalized feedback on their pitch accuracy and stability in real time while playing a chorale from the ChoraleBricks [1] dataset.

For additional information, visit the accompanying website.

Application Scenario 2: Interactive Singing Game

The second application scenario for the RT-SWIPE algorithm is an interactive singing game called "Sing Your Way" [4] designed to combine education and entertainment. This game challenges players to control a character in a virtual environment using their singing voice. By estimating the pitch of the player's voice in real time, the RT-SWIPE algorithm enables innovative gameplay mechanics, such as navigating through obstacles and interacting with the game world.

The accompanying video demonstrates Level 5 of the game, where players enter a flying mode controlled by their singing pitch. Players must smoothly transition between pitches to navigate through narrow gaps, offering a fun and engaging way to train vocal control and precision. While solving Level 5, the players might notice the famous four-note "short-short-short-long" motif from Ludwig van Beethoven's Symphony No. 5 in C minor, Op. 67.

For additional game levels, please visit the accompanying website.

Users Playing Level 5

References

1. Stefan Balke, Axel Berndt, and Meinard Müller
   ChoraleBricks: A Modular Multitrack Dataset for Wind Music Research
   Transactions of the International Society for Music Information Retrieval (TISMIR), 2025. Bibtex

   @article{BalkeBM24_ChoraleBricks_TISMIR,
   author  = {Stefan Balke and Axel Berndt and Meinard M{\"u}ller},
   title   = {{ChoraleBricks}: A Modular Multitrack Dataset for Wind Music Research},
   journal = {Transactions of the International Society for Music Information Retrieval ({TISMIR})},
   year    = {2025}
   }

2. Peter Meier, Meinard Müller, and Stefan Balke
   Analyzing Pitch Estimation Accuracy in Cross-Talk Scenarios: A Study with Wind Instruments
   In Proceedings of the Sound and Music Computing Conference (SMC): 3–10, 2025. Bibtex Details Demo DOI

   @inproceedings{MeierMB25_WindPitchEstimation_SMC,
   author    = {Peter Meier and  Meinard M{\"u}ller and Stefan Balke},
   title     = {Analyzing Pitch Estimation Accuracy in Cross-Talk Scenarios: {A} Study with Wind Instruments},
   booktitle = {Proceedings of the Sound and Music Computing Conference ({SMC})},
   address   = {Graz, Austria},
   year      = {2025},
   pages     = {3--10},
   doi       = {10.5281/zenodo.15835032},
   url-demo  = {https://www.audiolabs-erlangen.de/resources/MIR/2025-SMC-PitchCrosstalk},
   url-details={https://zenodo.org/records/15835033}
   }

3. Peter Meier, Meinard Müller, and Stefan Balke
   A Multi-User Interface for Real-Time Intonation Monitoring in Music Ensembles
   In Proceedings of the Workshop for Innovative Computer-based Music Interfaces (ICMI): 1–5, 2025. Bibtex

   @inproceedings{MeierMB25_IntonationMonitoring_ICMI,
   author      = {Peter Meier and Meinard M{\"u}ller and Stefan Balke},
   title       = {A Multi-User Interface for Real-Time Intonation Monitoring in Music Ensembles},
   booktitle   = {Proceedings of the Workshop for Innovative Computer-based Music Interfaces ({ICMI})},
   address     = {Chemnitz, Germany},
   year        = {2025},
   pages       = {1--5},
   }

4. Peter Meier, Simon Schwär, Gerhard Krump, and Meinard Müller
   Evaluating Real-Time Pitch Estimation Algorithms for Creative Music Game Interaction
   In: INFORMATIK 2023 — Designing Futures: Zukünfte gestalten, Gesellschaft für Informatik e.V.: 873–882, 2023. Bibtex DOI

   @incollection{MeierSKM23_EvaluatingPitchGame_GI,
   author    = {Peter Meier and Simon Schw{\"a}r and Gerhard Krump and Meinard M{\"u}ller},
   title     = {Evaluating Real-Time Pitch Estimation Algorithms for Creative Music Game Interaction},
   booktitle = {INFORMATIK 2023 -- Designing Futures: Zuk{\"u}nfte gestalten},
   publisher = {Gesellschaft f{\"u}r Informatik e.V.},
   address   = {Bonn, Germany},
   year      = {2023},
   pages     = {873--882},
   doi       = {10.18420/inf2023_97},
   }

Acknowledgments

The International Audio Laboratories Erlangen, Germany, are a joint institution of the Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) and Fraunhofer Institute for Integrated Circuits IIS. This work was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under grant numbers 500643750 (MU 2686/15-1) and 555525568 (MU 2686/18-1).