DLS media type: Media Type Registrations for Downloadable Sounds for Musical Instrument Digital Interface (MIDI)
Official media type designation for downloadable sound instruments used in MIDI synthesis.
Frojdh, P., Lindgren, U., and M. Westerlund, "Media Type Registrations for Downloadable Sounds for Musical Instrument Digital Interface (MIDI)", RFC 4613, DOI 10.17487/RFC4613, September 2006, <https://www.rfc-editor.org/info/rfc4613>.
@misc{rfc4613,
series = {Request for Comments},
number = 4613,
howpublished = {RFC 4613},
publisher = {RFC Editor},
doi = {10.17487/RFC4613},
url = {https://www.rfc-editor.org/info/rfc4613},
author = {P. Frojdh and U. Lindgren and M. Westerlund},
title = {{Media Type Registrations for Downloadable Sounds for Musical Instrument Digital Interface (MIDI)}},
pagetotal = 6,
year = 2006,
month = sep,
} RFC text
Contents
Network Working Group P. Frojdh
Request for Comments: 4613 U. Lindgren
Category: Informational M. Westerlund
Ericsson
September 2006
Media Type Registrations for Downloadable Sounds
for Musical Instrument Digital Interface (MIDI)
Status of This Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
This document serves to register a media type for Downloadable
Sounds.
Table of Contents
1. Introduction ....................................................1
2. Security Considerations .........................................2
3. IANA Considerations .............................................2
3.1. Media Type for Downloadable Sounds .........................3
4. References ......................................................5
4.1. Normative References .......................................5
4.2. Informative References .....................................5
1. Introduction
The present document seeks to register a media type for Downloadable
Sounds (DLSes). The DLS format is used to define instruments for
widely used wavetable synthesizers associated with the standards
[DLS1, DLS2, MDLS]. DLSes and their associated standards are
maintained and defined by two organizations, the Musical Instrument
Digital Interface (MIDI) Manufacturers Association (MMA) and the
Association of the Musical Electronics Industry (AMEI).
The media type defined here is needed to identify DLS files correctly
when they are served over HTTP, included in multi-part documents, or
used in other places where media types are used.
2. Security Considerations
The DLS format may contain audio, displayable text data, and modeling
parameters (a.k.a. articulation parameters). In addition, the DLS
format contains a so-called conditional chunk that is 'active' in the
sense that it affects the execution of a DLS file parser. However,
the DLS format does not currently define any scripting mechanism.
Clearly, it is possible to author malicious files that, for example,
contain large amounts of data always blocked by a conditional
statement; i.e., no synthesizer loads the instruments.
However, for DLS, clients can and usually do protect themselves
against these kinds of attacks. A key point is that conditional
chunks are optional, that is, a parser does not have to execute a
conditional chunk. However, if a parser evaluates a conditional
chunk, it is still possible to parse its content and draw to a
conclusion as to whether it is usable for a particular synthesizer
engine.
Note that selected metadata fields may include information partly
intended to protect the media against unauthorized use or
distribution. In this case, the intention is that alteration or
removal of the data in the field would be treated as an offense under
national agreements based on World Intellectual Property Organization
(WIPO) treaties.
DLS have an extensible structure, making it theoretically possible to
define metadata fields or media formats in the future that could be
used to induce particular actions of the recipient, and thus that
would present additional security risks. However, this type of
capability is currently not supported in the referenced
specifications.
There is no current provision in the DLS standard for encryption,
signing, or authentication within the file formats.
3. IANA Considerations
The IANA has registered the media type audio/dls, as specified in
Section 3.1. The registration uses the template present in
[RFC4288].
3.1. Media Type for Downloadable Sounds
Type name: audio
Subtype name: dls
Required parameters: None
Optional parameters: 'dls-type'
A comma-separated list of the
dls types (one or more) that the
file content conforms to. The
following values are specified:
0, 1, and 2 signify Downloadable
Sounds Level 1.1b content,
Downloadable Sounds Level 2.1
content, and Mobile Downloadable
Sound content, respectively. All
types that the content conforms
to should be indicated. Further
values (integers) may be
specified in the future, and any
unknown values shall be ignored.
If the parameter is not
specified, it corresponds to a
value equal to 0; i.e., the
content conforms to Downloadable
Sound level 1.1b.
Encoding considerations: DLS files are binary and should
be transmitted in a suitable
encoding without CR/LF
conversion, 7-bit stripping
etc.; base64 [RFC3548] is a
suitable encoding.
Security considerations: see the security considerations
in Section 2 of RFC 4613.
Interoperability considerations: This media type is for
consumption by a MIDI player
capable of utilizing
downloadable sounds for its
synthesizers. A general-purpose
audio player will not be capable
of utilizing the audio within
the format without explicit
support of the format.
Published specification: Downloadable Sounds Level 1.1b
[DLS1], Downloadable Sounds
Level 2.1 [DLS2], and Mobile
Downloadable Sounds [MDLS]. MMA
specifications can be ordered
from the MMA web site,
www.midi.org.
Applications that use this media type: Multi-media
Additional information:
Magic number(s): The ninth to twelfth bytes of
the file must equal (in
hexadecimal notation) 44, 4c,
53, and 20, respectively.
File extension(s): .dls is declared at
http://www.nist.gov/nics
Person & email address to contact for further information:
Ulf A. Lindgren,
ulf.a.lindgren@ericsson.com
Intended usage: COMMON
Restrictions on usage: None
Author: Per Frojdh
Ulf A. Lindgren
Magnus Westerlund
Change controller: MIDI Manufacturers Association
http://www.midi.org
info@midi.org
4. References
4.1. Normative References
[DLS1] "Downloadable Sounds Level 1.1b", MMA/AMEI specification
v1.1b, Los Angeles, CA, USA, 2004.
[DLS2] "Downloadable Sounds Level 2.1", MMA/AMEI specification
v1.0, Los Angeles, CA, USA, 2001.
[MDLS] "Mobile Downloadable Sounds 1.0", MMA specification v1.0,
Los Angeles, CA, USA, 2004.
[RFC4288] Freed, N. and J. Klensin, "Media Type Specifications and
Registration Procedures", BCP 13, RFC 4288, December 2005.
4.2. Informative References
[RFC3548] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 3548, July 2003.
Authors' Addresses
Per Frojdh
Ericsson AB
Ericsson Research
SE-164 80 Stockholm
Sweden
EMail: per.frojdh@ericsson.com
Ulf A. Lindgren
Ericsson AB
Ericsson Research
SE-417 56 Goteborg
Sweden
EMail: ulf.a.lindgren@ericsson.com
Magnus Westerlund
Ericsson AB
Ericsson Research
SE-164 80 Stockholm
Sweden
EMail: magnus.westerlund@ericsson.com
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AI ELI5
On this page
§1What Downloadable Sounds Are
Downloadable Sounds (DLS) is a file format used to define instruments for wavetable synthesizers associated with MIDI (Musical Instrument Digital Interface) standards. DLS files are maintained and defined by two organizations: the MIDI Manufacturers Association (MMA) and the Association of the Musical Electronics Industry (AMEI).
DLS format comes in three levels: DLS Level 1.1b, DLS Level 2.1, and Mobile Downloadable Sounds. These standards allow programs to package instrument definitions in a portable format. Before this media type registration, there was no standardized way to identify DLS files when they were served over HTTP, included in multi-part email messages, or used in other contexts where media types matter.
DLS files are like recipe cards for music. They tell the computer how to make different instrument sounds. Now there's an official name for them, just like "photo" or "song".
§2Media Type Registration
The registered media type is audio/dls. It has one optional parameter: dls-type, which specifies the DLS version levels the file conforms to. The parameter accepts comma-separated values: 0 for DLS Level 1.1b, 1 for DLS Level 2.1, and 2 for Mobile Downloadable Sounds. Multiple values can be listed if the file conforms to multiple levels. If the parameter is not specified, it defaults to level 0 (DLS Level 1.1b).
DLS files are binary files and must be transmitted without CR/LF conversion or 7-bit stripping; Base64 encoding is recommended. The registered file extension is .dls.
The official name is audio/dls. You can add a note saying which version of the format it uses, but if you don't, it assumes the basic version.
§3Security Issues with DLS Files
DLS files can contain audio data, displayable text, and modeling parameters (articulation parameters). Additionally, DLS format includes a conditional chunk that is active, meaning it affects how a DLS file parser executes. However, the DLS format does not currently support scripting mechanisms.
Conditional chunks in DLS are optional, so a parser need not execute them. If a parser does evaluate a conditional chunk, it can still parse its content and determine whether it is usable for a particular synthesizer engine. Malicious DLS files could theoretically contain large amounts of conditional data, but synthesizers typically protect themselves by parsing conditionally and safely.
DLS files support optional metadata fields that may protect content against unauthorized use under WIPO treaties. The format is extensible, making it theoretically possible to add new metadata in the future, but such capabilities are not currently supported.
DLS files could be tricky if someone tried to hide bad stuff in them, but music programs are designed to be safe. The files don't have scripts that run, so the worst they can do is waste space or ask for permission before loading bad data.
§4How DLS Files Are Used
The audio/dls media type is intended for consumption by a MIDI player capable of utilizing downloadable sounds for synthesizers. A general-purpose audio player will not be able to play the audio within a DLS file without explicit support for the format. DLS files are consumed by specialized MIDI applications, synthesizer control software, and multi-media systems that include MIDI playback capabilities.
The specifications for DLS levels are available from the MIDI Manufacturers Association (www.midi.org). The format has been used in commercial music production systems, mobile devices, and consumer electronics that include MIDI synthesis capabilities.
Only music programs that understand DLS can use these files. Your regular music player can't play them directly, but a MIDI synthesizer or music production program can use the instrument definitions they contain.