RFC 4613

Media Type Registrations for Downloadable Sounds for Musical Instrument Digital Interface (MIDI)

📅 published September 2006, from ietf

Media Type Registrations for Downloadable Sounds for Musical Instrument Digital Interface (MIDI) 🎹✨

Okay bestie, this one is RFC 4613 from September 2006, written by Per Frojdh, Ulf A. Lindgren, and Magnus Westerlund (all three from Ericsson 💅). It's Informational 🌸, which means it's giving info for the Internet community, not an official standard. It doesn't say it obsoletes or updates any other RFC, so it just stands on its own 🦋.

Status of This Memo 🎀

This memo provides information for the Internet community. It is not an Internet standard of any kind, and distribution of it is unlimited 🌈.

Copyright Notice 💜

Abstract 🍓

This document registers a media type for Downloadable Sounds, so you can actually label these files properly 🧚.

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 🌸

So the point of this doc is to register a media type for Downloadable Sounds (DLSes) 🎶. The DLS format is used to define instruments for wavetable synthesizers that follow the standards [DLS1, DLS2, MDLS]. Two orgs maintain and define DLS and its related standards: the Musical Instrument Digital Interface (MIDI) Manufacturers Association (MMA) and the Association of the Musical Electronics Industry (AMEI) 💖.

The media type is needed so DLS files get identified correctly whenever they're served over HTTP, included in multi-part documents, or used anywhere else media types show up 🦋✨.

2. Security Considerations 🔥

Okay this section is serious, so read it carefully 🫶. A DLS file can contain audio, displayable text data, and modeling parameters (a.k.a. articulation parameters) 🎧. The DLS format also has a so-called conditional chunk that is 'active', which means it affects how a DLS file parser runs 👀. The thing is, DLS doesn't currently define any scripting mechanism 💅.

Clearly it's possible to author malicious files that, for example, contain large amounts of data that always get blocked by a conditional statement. In other words, no synthesizer loads the instruments 💀.

BUT, for DLS, clients can and usually do protect themselves against these kinds of attacks 🛡️. The key point is that conditional chunks are optional, so a parser does not have to execute a conditional chunk. Even so, if a parser does evaluate a conditional chunk, it's still possible to parse its content and figure out whether it's usable for a particular synthesizer engine 🎹.

Also, selected metadata fields may include information partly meant to protect the media against unauthorized use or distribution. In that case, the intention is that altering or removing the data in that field would be treated as an offense under national agreements based on World Intellectual Property Organization (WIPO) treaties 🙈⚖️.

DLS has an extensible structure, so it's theoretically possible that future metadata fields or media formats could be defined to induce particular actions in the recipient. That kind of capability would bring extra security risks 😭. Right now though, this type of capability is not supported in the referenced specifications 🙌.

And there's no current provision in the DLS standard for encryption, signing, or authentication within the file formats. So just keep that in mind 🔐💜.

3. IANA Considerations 🧚

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 🎵

Here's the full registration, copied exactly 💅:

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

Full Copyright Statement 🌈

This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights.

This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

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Acknowledgement 🧚‍♀️

Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA) 👑.

📦 where this page comes from

ietf: rfc4613 2006-09
💖 girlified by claude-haiku-5-5 on 2026-10-16: a language model's rewrite of the original, under its terms