aseqdump

aseqdump [options]

-p, --port <client:port>
    Specifies the ALSA sequencer port to listen on. This can be a numerical identifier (e.g., 128:0) or a port name (e.g., Midi Through:0). Use aconnect -l to list available ports.

-t, --timestamp
    Prints a timestamp for each received MIDI event, showing the time elapsed since aseqdump started. This helps in analyzing event timing.

-R, --raw
    Displays the raw MIDI event bytes in hexadecimal format instead of the human-readable interpreted format. Useful for low-level debugging.

-c, --channel <N>
    Filters and displays only MIDI events occurring on the specified MIDI channel (0-15). This can help in focusing on specific data streams.

-u, --unparseable
    Includes unparseable events in the output. This option is typically used for debugging the ALSA sequencer itself, revealing malformed or unknown events.

-i, --input <filename>
    Reads MIDI events from a specified raw MIDI file instead of a live sequencer port. Useful for analyzing pre-recorded MIDI data.

-o, --output <filename>
    Writes the received MIDI events to a specified raw MIDI file. Can be used for logging or capturing MIDI streams.

-s, --sync
    Synchronizes event output with real-time, particularly when reading from a file, ensuring events are printed at their original relative times.

-h, --help
    Displays a brief help message with available command-line options.

-v, --version
    Shows the version information of the aseqdump utility.

aseqdump is a powerful utility from the ALSA (Advanced Linux Sound Architecture) project, designed to monitor and display MIDI sequencer events. It functions by listening on a specified ALSA MIDI sequencer port (or a default 'dump' port created by the command itself) and printing all received MIDI events to standard output in a human-readable format. This command is an invaluable tool for debugging MIDI applications, understanding the flow of MIDI signals within your Linux system, or simply observing real-time MIDI traffic. The output typically includes detailed information such as event timestamps, source and destination port details, the type of MIDI event (e.g., Note On, Control Change, Program Change), and the associated data for each event. It acts as a transparent window into your system's MIDI communication.

aseqdump is an observation tool and not designed for real-time performance-critical applications. While it processes events efficiently, its output to standard I/O might introduce minor latency. Ensure the target ALSA sequencer port is available and correctly specified; use aconnect -l to verify port existence. For high-volume MIDI traffic, the output can be very verbose and scroll rapidly, often requiring piping to tools like less or grep for effective analysis.

This command is exceptionally useful for verifying the correct flow of MIDI data between different applications (e.g., MIDI controllers, software synthesizers, Digital Audio Workstations). By strategically connecting aseqdump at various points in the MIDI signal chain using aconnect, users can effectively isolate and diagnose where MIDI events might be getting dropped, delayed, or malformed.

Beyond mere debugging, aseqdump can be used for general MIDI monitoring. It allows users to gain deep insight into the actual MIDI messages being generated by a connected MIDI device or received by an application, which is invaluable for understanding the specifics of the MIDI protocol and device behavior.

aseqdump is a long-standing component of the alsa-utils package, which provides essential command-line utilities for the ALSA sound system in Linux. Its development is deeply intertwined with the evolution of ALSA itself, making it a foundational tool for MIDI diagnostics and monitoring within the Linux audio ecosystem. It has consistently provided a robust and reliable method for inspecting ALSA sequencer event streams across various Linux distributions for many years.

aconnect(1), aplaymidi(1), arecordmidi(1), amidi(1)