您要查找的是不是:
['wu:f?(r)]
低音用扩音器
低音扬声器；
低音喇叭；
低音音箱；
大家都在背：
1. By 2003, TC Sound was producing the luxury class woofer chassis for Ground Zero.
到2003年, TCSound一直都在为GroundZero生产奢侈档次的低音机箱.
来自互联网
2. Selecting OFF mutes the sound of the LFE channel from the sub woofer.
选择“关闭”可关闭来自低音炮的LFE声道的声音.
来自互联网
1. a loudspeaker that reproduces lower audio frequency sounds
1. 低音扬声器
石油英语词汇(W2)|生物化学专业英语词汇 ... woof 纬；织物；基本材料 woofer 低音扬声器 wool type fiber 毛型纤维.
- 基于424个网页
2. 低音喇叭
　　5.低音喇叭（woofer） ——要表现音乐的神韵，优质的低音喇叭绝对不可缺少。　　根据 GFK 的最新研究显示,国产品牌的市场占有率 …
- 基于132个网页
3. 低音音箱
专业音频术语中英文对照 ... Wole Tone 不协和调 Woofer 低音音箱 WORM write once read many 一次写入型光盘.
- 基于132个网页
4. 低音单元
低音单元（Woofer）： 一种驱动单元只为在低频中工作而设计，在二路分音系统中所谓的低音单元多数应称为中/低音单元才更合当。 …
- 基于89个网页
1. 低音驱动器
woofer driver : 10 " , acustically transparent high moulded aluminium basket , 80 oz magnet , rubber suspension , treated non pressed paper cone . "低音驱动器：10“，透声高流动性铝铸盆架，80盎司重磁体，橡胶盆架，高温处理松压纸盆。
- 基于3个网页
1. 重低音输出
TA8218H - 电子综合 - 技术资料== ... NC 未用 WOOFER OUT 重低音输出 MUTE2 静音控制.
- 基于2个网页
1. 次级低音扬声器
10/20 的英文课 : Bajillion of idioms!!! @... ... 10. nerd = 宅男 sub woofer 次级低音扬声器 Mark 2 同学提出的问题.
- 基于5个网页
1. 超重音箱
...质量的核心所在。同时，喇叭、分音扩大器(AMP)、超重音箱(Sub woofer)等也对音响的整体效果有重大影响，如果忽视其中的任何 …
- 基于19个网页
SW输出要在菜单里设置一下，打开低音炮(SUB WOOFER)选项求助知友cqzaodian |六级采纳率24% 擅长领域：暂未定制
- 基于12个网页
0){var rand = parseInt(Math.random() * (000)+100000);top.location.href='/'+encodeURIComponent(document.getElementById('s').value.trim().replace( / /g, '_'))+'?renovate='+}else{top.location.href='/'+encodeURIComponent(document.getElementById('s').value.trim().replace( / /g, '_'));};}" action="/">
查过的词自动加入生词本
Tip：此功能设置只能在登录状态下生效
需要改进的内容：
单词大小写
其他（请在下面补充描述）
错误描述：
您还可在这里补充说明下 O(∩_∩)O~
方便的话，请您留下一种联系方式，便于问题的解决：sub-woofer的音箱是什么牌子?_百度知道
sub-woofer的音箱是什么牌子?
提问者采纳
近年由于AV的普及，加上多媒体 (Multi-media)计算机的飞速发展，越来越多人家里添置了超重低音音箱，在香港我们一般称它为超低音(Sub-woofer)，但在国内，普遍会叫超重低音，更或有人称之为低音炮。有一次我在深圳的电子商场见到一位北方来客正在查询超低音的价格性能，当店员给他指点几款方型的超低音时，他惊异地说：“怎么不是大炮（圆管状？）的样子的？？”，我想这大概是由于BOSE宣传它的Cannon太深入人心吧。
其他类似问题
为您推荐：
sub的相关知识
等待您来回答
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随时随地咨询
出门在外也不愁woofer_百度作业帮
翻译为：低声立体扬声器希望能够帮到你!
woofer stereo低音音响您要查找的是不是:
['wu:f?(r)]
低音用扩音器
低音扬声器；
低音喇叭；
低音音箱；
大家都在背：
1. By 2003, TC Sound was producing the luxury class woofer chassis for Ground Zero.
到2003年, TCSound一直都在为GroundZero生产奢侈档次的低音机箱.
来自互联网
2. Selecting OFF mutes the sound of the LFE channel from the sub woofer.
选择“关闭”可关闭来自低音炮的LFE声道的声音.
来自互联网
1. a loudspeaker that reproduces lower audio frequency sounds
1. 低音扬声器
石油英语词汇(W2)|生物化学专业英语词汇 ... woof 纬；织物；基本材料 woofer 低音扬声器 wool type fiber 毛型纤维.
- 基于424个网页
2. 低音喇叭
　　5.低音喇叭（woofer） ——要表现音乐的神韵，优质的低音喇叭绝对不可缺少。　　根据 GFK 的最新研究显示,国产品牌的市场占有率 …
- 基于132个网页
3. 低音音箱
专业音频术语中英文对照 ... Wole Tone 不协和调 Woofer 低音音箱 WORM write once read many 一次写入型光盘.
- 基于132个网页
4. 低音单元
低音单元（Woofer）： 一种驱动单元只为在低频中工作而设计，在二路分音系统中所谓的低音单元多数应称为中/低音单元才更合当。 …
- 基于89个网页
1. 低音驱动器
woofer driver : 10 " , acustically transparent high moulded aluminium basket , 80 oz magnet , rubber suspension , treated non pressed paper cone . "低音驱动器：10“，透声高流动性铝铸盆架，80盎司重磁体，橡胶盆架，高温处理松压纸盆。
- 基于3个网页
1. 重低音输出
TA8218H - 电子综合 - 技术资料== ... NC 未用 WOOFER OUT 重低音输出 MUTE2 静音控制.
- 基于2个网页
1. 次级低音扬声器
10/20 的英文课 : Bajillion of idioms!!! @... ... 10. nerd = 宅男 sub woofer 次级低音扬声器 Mark 2 同学提出的问题.
- 基于5个网页
1. 超重音箱
...质量的核心所在。同时，喇叭、分音扩大器(AMP)、超重音箱(Sub woofer)等也对音响的整体效果有重大影响，如果忽视其中的任何 …
- 基于19个网页
SW输出要在菜单里设置一下，打开低音炮(SUB WOOFER)选项求助知友cqzaodian |六级采纳率24% 擅长领域：暂未定制
- 基于12个网页
0){var rand = parseInt(Math.random() * (000)+100000);top.location.href='/'+encodeURIComponent(document.getElementById('s').value.trim().replace( / /g, '_'))+'?renovate='+}else{top.location.href='/'+encodeURIComponent(document.getElementById('s').value.trim().replace( / /g, '_'));};}" action="/">
查过的词自动加入生词本
Tip：此功能设置只能在登录状态下生效
需要改进的内容：
单词大小写
其他（请在下面补充描述）
错误描述：
您还可在这里补充说明下 O(∩_∩)O~
方便的话，请您留下一种联系方式，便于问题的解决：Network Working Group
K. Kobayashi
Request for Comments: 3190
Communication Research Laboratory
Category: Standards Track
Keio University
Packet Design
C. Bormann
Universitaet Bremen TZI
January 2002
RTP Payload Format for
12-bit DAT Audio and 20- and 24-bit Linear Sampled Audio
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements.
Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol.
Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2002).
All Rights Reserved.
This document specifies a packetization scheme for encapsulating
12-bit nonlinear, 20-bit linear, and 24-bit linear audio data streams
using the Real-time Transport Protocol (RTP).
This document also
specifies the format of a Session Description Protocol (SDP)
parameter to indicate when audio data is preemphasized before
The parameter may be used with other audio payload
formats, in particular L16 (16-bit linear).
1. Introduction
This document describes the sampling of audio data in 12-bit
nonlinear, 20-bit linear, and 24-bit linear encodings, and specifies
the encapsulation of the audio data into the Real-time Transport
Protocol (RTP), version 2 [1,2].
DAT (digital audio tape) and DV
(digital video) devices [3,4] use these audio encodings in addition
to 16-bit linear encoding.
The packetization scheme for 16-bit
linear audio (L16) is already specified [2,5].
This document
specifies the packetization scheme for the other encodings following
that for L16; in particular, when used with the RTP profile [2],
these payload formats follow the encoding-independent rules for
Kobayashi, et al.
Standards Track
RTP Payload Format
January 2002
sample ordering and channel interleaving specified in [2] plus
extensions specified here.
This document also specifies out-of-band
negotiation methods for the extended channel interleaving rules and
for use when an analog preemphasis technique is applied to the audio
1.1 Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [6]
2. The need for RTP encapsulation of 12-, 20- and 24-bit audio
Many high-quality digital audio and visual systems, such as DAT and
DV, adopt sample-based audio encodings.
Different audio formats are
used in various situations.
To transport the audio data using RTP,
an encapsulation needs to be defined for each specific format.
16-bit linear audio encapsulation (L16) has thus far been defined.
Other encoding formats have already appeared, such as the 12-bit
nonlinear, 20-bit linear and 24-bit linear encodings used in the DAT
and DV video world.
This specification defines the RTP payload
encapsulation format in order to use the new encodings in the RTP
environment.
3. 12-bit nonlinear audio encapsulation
IEC 61119 [3] specifies the 12-bit nonlinear audio format in DAT and
DV, called LP (Long Play) audio.
It would be easy to convert 12-bit
nonlinear audio into 16-bit linear form at the RTP sender and
transmit it using the L16 audio format already defined.
this would consume 33% more network bandwidth than necessary.
payload format is specified as a more efficient alternative.
The 12-bit nonlinear encoding is the same as for 16-bit linear audio
except for the packing of each sampled data element.
Each sample of
12-bit nonlinear audio is derived from a single sample of 16-bit
linear audio by a nonlinear compression.
Table 1 shows the details
of the conversion from 16 to 12 bits.
The result is a 12-bit signed
value ranging from -2048 to 2047 and it is represented in two's
complement notation.
The 12-bit samples are packed contiguously into
payload octets starting with the most significant bit.
payload contains an odd number of samples, the four LSBs of the last
octet are unused.
Parameters other than quantization, e.g., sampling
frequency and audio channel assignment, are the same as in the L16
payload format.
In particular, samples are packed into the packet in
time sequence beginning with the oldest sample.
Kobayashi, et al.
Standards Track
RTP Payload Format
January 2002
------------------------------------------------------------
32,767 (7FFFh) Y = INT(X/64) + (600h)
2,047 (7FFh)
16,384 (4000h)
1,792 (700h)
------------------------------------------------------------
16,383 (3FFFh) Y = INT(X/32) + (500h)
1,791 (6FFh)
8,192 (2000h)
1,536 (600h)
------------------------------------------------------------
8,191 (1FFFh) Y = INT(X/16) + (400h)
1,535 (5FFh)
4,096 (1000h)
1,280 (500h)
------------------------------------------------------------
4,095 (0FFFh) Y = INT(X/8) + (300h)
1,279 (4FFh)
2,048 (0800h)
1,024 (400h)
------------------------------------------------------------
2,047 (07FFh) Y = INT(X/4) + (200h)
1,023 (3FFh)
1,024 (0400h)
768 (300h)
------------------------------------------------------------
1,023 (03FFh) Y = INT(X/2) + (100h)
767 (2FFh)
512 (0200h)
512 (200h)
------------------------------------------------------------
511 (01FFh) Y = X
511 (1FFh)
------------------------------------------------------------
-1 (FFFFh) Y = X
-512 (FE00h)
-512 (E00h)
------------------------------------------------------------
-513 (FFFFh) Y = INT((X + 1)/2) - (101h)
-513 (DFFh)
-1,024 (FE00h)
-768 (D00h)
------------------------------------------------------------
-1,025 (FBFFh) Y = INT((X + 1)/4) - (201h)
-769 (CFFh)
-2,048 (F800h)
-1,024 (C00h)
------------------------------------------------------------
-2,049 (F7FFh) Y = INT((X + 1)/8) - (301h)
-1,025 (BFFh)
-4,096 (F000h)
-1,280 (B00h)
------------------------------------------------------------
-4,097 (EFFFh) Y = INT((X + 1)/16) - (401h) -1,281 (AFFh)
-8,192 (E000h)
-1,536 (A00h)
------------------------------------------------------------
-8,193 (DFFFh) Y = INT((X + 1)/32) - (501h) -1,537 (9FFh)
-16,384 (C000h)
-1,792 (900h)
------------------------------------------------------------
-16,385 (BFFFh) Y = INT((X + 1)/64) - (601h) -1,793 (8FFh)
-32,768 (8000h)
-2,048 (800h)
------------------------------------------------------------
Table 1. Conversion from 16-bit linear values (X) to 12-bit
nonlinear values (Y) [3]
Kobayashi, et al.
Standards Track
RTP Payload Format
January 2002
When conveying encoding information in an SDP [7] session
description, the 12-bit nonlinear audio payload format specified here
is given the encoding name "DAT12".
Thus, the media format
representation might be:
m=audio 49230 RTP/AVP 97 98
a=rtpmap:97 DAT12/32000/2
a=rtpmap:98 L16/48000/2
4. 20- and 24-bit linear audio encapsulation
The 20- and 24-bit linear audio encodings are simply an extension of
the L16 linear audio encoding [2].
The 20- or 24-bit uncompressed
audio data samples are represented as signed values in two's
complement notation.
The samples are packed contiguously into
payload octets starting with the most significant bit.
20-bit encoding, when the payload contains an odd number of samples,
the four LSBs of the last octet are unused.
Samples are packed into
the packet in time sequence beginning with the oldest sample.
When conveying encoding information in an SDP session description,
the 20- and 24-bit linear audio payload formats specified here are
given the encoding names "L20" and "L24", respectively.
An example
SDP audio media description would be:
m=audio 49230 RTP/AVP 99 100
a=rtpmap:99 L20/48000/2
a=rtpmap:100 L24/48000
5. Preemphasized audio data
In order to improve the higher frequency characteristics of audio
signals, analog preemphasis is often applied to the signal before
quantization.
If analog preemphasis was applied before the payload
data was sampled, the type of the preemphasis SHOULD be conveyed with
out-of-band signaling.
An "emphasis" parameter is defined for this
purpose and may be conveyed either as a MIME optional parameter or
using the SDP format-specific attribute (a=fmtp line) as below:
a=fmtp: emphasis=
value is defined for the parameter at this
Kobayashi, et al.
Standards Track
RTP Payload Format
January 2002
The emphasis attribute MUST NOT be included in the SDP record if
preemphasis was not applied.
This rule allows the emphasis attribute
to be used with other audio formats, in particular L16 [2], while
retaining backward compatibility with existing implementations so
long as preemphasis is not applied.
If an existing application that
does not implement preemphasis accepts a session description with an
emphasis attribute but ignores that attribute, the only penalty is
that the sound will be too "bright" when receiving or "dull" when
A sample SDP record showing preemphasis applied only to payload type
99 might be as follows:
m=audio 49230 RTP/AVP 99 100
a=rtpmap:99 L20/48000/2
a=fmtp:99 emphasis=50-15
a=rtpmap:100 L24/48000
6. Translation of DV audio error code
The DV video specification IEC ] defines the negative full-
scale audio sample value to be an audio error code indicating that no
valid audio sample is available for that sample period.
error might occur due to a failure while reading audio data from
magnetic tape.
The audio error code values for each of the DV audio
encodings are (in hexadecimal):
12-bit nonlinear:
16-bit linear:
20-bit linear:
For the payload formats defined in this document, as well as for the
L16 payload format defined in [2], no such error code is defined.
That is, all possible sample values are valid.
When an RTP sender
accepts audio samples from a DV video system and encapsulates those
samples according to one of these payload formats, the RTP sender
SHOULD perform some error concealment algorithm which may depend upon
whether a single sample error or multiple sample errors have
The error concealment algorithm is not specified here and
is left to the implementation.
The RTP sender MAY treat the error
code as if it were a valid audio sample, but this is likely to cause
undesirable audio output.
Conversely, an RTP receiver that accepts audio packets in one of
these payload formats and delivers the audio samples to a DV video
system SHOULD translate the audio samples that would be interpreted
as error codes into the next smaller negative audio value.
audio samples may be present because the audio packets may have come
Kobayashi, et al.
Standards Track
RTP Payload Format
January 2002
from a source other than a DV video system.
The DV video
specification [4] gives the following translations for the defined
audio encodings:
12-bit nonlinear:
16-bit linear:
20-bit linear:
80000h - 8000Fh
For the 20-bit linear encoding, note that multiple audio sample
values are translated in order to allow a 16-bit system to play 20-
bit audio data by ignoring the least significant four bits.
also that no translation is specified for 24-bit linear audio because
that encoding is not included in the DV video specification.
7. Channel interleaving and non-AIFF-C audio channel convention
When multiple channels of audio, such as in a stereo program, are
multiplexed into a single RTP stream, the audio samples from each
channel are interleaved according to the rules specified in [2] to be
consistent with the L16 payload format.
That is, samples from
different channels taken at the same sampling instant are packed into
consecutive octets.
For example, for a two-channel encoding, the
sample sequence is (left channel, first sample), (right channel,
first sample), (left channel, second sample), (right channel, second
Samples for all channels belonging to a single sampling
instant MUST be contained in the same packet.
This sample order differs from the packing of samples into blocks in
a native DV audio stream.
Therefore, applications transmitting DV
audio using the payload formats defined in this document MUST
reshuffle the samples into the order specified here.
requirement is intended to enable interworking between DV systems and
other digital audio systems.
Applications choosing to send bundled
DV audio/video streams using the native DV block structure may use
the payload format defined in [8] instead.
Most of the existing RTP audio payload formats follow the AIFF-C
convention for channel ordering as specified in [2] when sending more
than two audio channels within a single RTP stream.
However, this
convention does not cover some applications.
For example, some DV
audio formats define a "woofer" channel, but AIFF-C does not include
this frequency-dependent channel.
Thus, it is necessary to specify
the audio channel allocation information explicitly when the contents
of the audio stream are beyond the scope of AIFF-C.
For DV audio streams of 4 or more channels, the channel order MUST be
specified out-of-band.
This applies both to the payload formats
defined in this document and to the L16 payload format.
A "channel-
Kobayashi, et al.
Standards Track
RTP Payload Format
January 2002
order" parameter is defined here for this purpose and may be conveyed
either as a MIME optional parameter or with the SDP a=fmtp attribute
using the following syntax:
a=fmtp: channel-order=.
The first component of the value, , specifies the type of
channel assignment convention used.
This allows for conventions
other than AIFF-C and DV to be defined in the future.
This document
defines only one convention for use in the channel-order parameter:
The second component of the value, , indicates the arrangement
of channels within the stream.
The DV video specification [4]
defines the types of audio channels that may be present and in what
The symbols used to denote the channel types are reproduced
in the Appendix at the end of this document.
For the DV convention,
the following values, which were formed from the concatenation of the
individual channel symbols in the allowed channel orders, are defined
component:
4 channels: LRLsRs, LRCS, LRCWo
5 channels: LRLsRsC
6 channels: LRLsRsCS, LmixRmixTWoQ1Q2
8 channels: LRCWoLsRsLmixRmix, LRCWoLs1Rs1Ls2Rs2, LRCWoLsRsLcRc
symbols are case-insensitive, but are
shown here in mixed case to make the individual channel symbols more
These concatenated symbols were deliberately constructed
without separators to make clear the fact that the channels MUST NOT
be assembled in other, arbitrary orders.
For interworking with DV video systems, some of the audio encodings
are defined only for a subset of the channel combinations listed
The DV video specification lists the channel combinations
that are allowed for each encoding.
The channel-order parameter MUST be consistent with the number of
channels specified in the MIME optional parameter "channels" or in
the a=rtpmap attribute of SDP.
For RTP audio streams of 1, 2 or 3
channels, the AIFF-C channel order is used and is implicit in the
number of audio channels specified.
To allow backward compatibility,
the channel-order parameter MUST NOT be included in this case.
Note that for the DV convention with 5 channels only one channel
order is allowed, but for consistency the channel-order parameter
MUST be included nonetheless.
Kobayashi, et al.
Standards Track
RTP Payload Format
January 2002
An example of an SDP session description using the channel-order
parameter is:
IN IP4 126.16.64.4
s=POI (Audio only)
i=A Seminar on making Presentations on the Internet
u=http://www.koganei.wide.ad.jp/~ikob/POI/index.html
e=ikob@koganei.wide.ad.jp (Katsushi Kobayashi)
c=IN IP4 224.2.17.12/127
m=audio 49170 RTP/AVP 112 113
a=rtpmap:112 L16/48000/2
a=rtpmap:113 DAT12/32000/4
a=fmtp:113 emphasis=50-15; channel-order=DV.LRCWO
This session description shows the audio medium being transmitted in
two formats, L16 and DAT12, using payload type numbers 112 and 113,
respectively.
For the L16 format, the audio data contains 2-channel
stereo following the implicit, default AIFF-C convention for left
channel first and right channel second.
For the DAT12 format, the
audio data contains 4 channels following the DV audio convention for
the channels left, right, center, and woofer.
This example also shows how multiple MIME optional parameters
("emphasis" and "channel-order") for these payload formats are mapped
to a single a=fmtp attribute as a semicolon separated list of
parameter=value pairs.
The channel-order parameter described here provides a generic out-of-
band mechanism to define alternatives to the AIFF-C channel order.
However, if multi-channel audio data could be sent following the
AIFF-C channel convention after simple processing, such as a data
shuffling on the sender side, the alternative channel order SHOULD
NOT be defined and instead the AIFF-C order SHOULD be employed to
maximize interoperability.
Moreover, multiple channels of audio data should only be multiplexed
within a single RTP stream when all of the audio channels are
intended to be reproduced together, such as the left and right
channels in a stereo program.
Independent audio channels, such as
multiple language translations, SHOULD be sent in separate RTP
This reduces bandwidth requirements by allowing receivers
to tune in to only those channels which are desired.
Kobayashi, et al.
Standards Track
RTP Payload Format
January 2002
8. MIME registration
This document defines some new RTP payload format names which are
also registered as MIME subtypes: DAT12, L20 and L24.
registration forms for these MIME subtypes are provided in the next
8.1 MIME registration form for audio/DAT12
MIME media type name: audio
MIME subtype name: DAT12
Required parameters:
rate: number of samples per second -- RECOMMENDED values for rate
are , 1, 2, 44100 and 48000
samples per second.
Other values are permissible.
Optional parameters:
channels: how many audio streams are interleaved -- defaults to 1;
stereo would be 2, etc.
Interleaving takes place between
individual 12-bit samples.
emphasis: analog preemphasis applied to the data before
quantization.
The only emphasis value defined here is
emphasis=50-15 to indicate 50/15 microsecond preemphasis.
parameter MUST be omitted if no analog preemphasis was applied.
channel-order: specifies the sample interleaving order for
multiple-channel audio streams (see RFC 3190 Section 7).
Permissible values are DV.LRLsRs, DV.LRCS, DV.LRCWo,
DV.LRLsRsC, DV.LRLsRsCS, DV.LmixRmixTWoQ1Q2,
DV.LRCWoLsRsLmixRmix, DV.LRCWoLs1Rs1Ls2Rs2, DV.LRCWoLsRsLcRc.
For interoperation with DV video systems, only a subset of
these channel combinations is specified for use with 12-bit
nonlinear encoding in the DV video specification [4]; that
subset is all of the above except DV.LmixRmixTWoQ1Q2.
parameter MUST be omitted when the AIFF-C channel order
convention is in use.
Encoding considerations:
DAT12 audio can be transmitted with RTP as specified in RFC 3190.
Security considerations: See Section 9.
Interoperability considerations: NONE
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Published specification:
IEC 61119 Standard [4] and RFC 3190.
Applications which use this media type:
Audio communication.
Additional information:
Magic number(s): None
File extension(s): None
Macintosh File Type Code(s): None
Person & email address to contact for further information:
Katsushi Kobayashi
e-mail: ikob@koganei.wide.ad.jp
Intended usage: COMMON
Author/Change controller:
Katsushi Kobayashi
e-mail: ikob@koganei.wide.ad.jp
8.2 MIME registration form for audio/L20
MIME media type name: audio
MIME subtype name: L20
Required parameters:
rate: number of samples per second -- RECOMMENDED values for rate
are , 1, 2, 44100 and 48000
samples per second.
Other values are permissible.
Optional parameters:
channels: how many audio streams are interleaved -- defaults to 1;
stereo would be 2, etc.
Interleaving takes place between
individual 20-bit samples.
emphasis: analog preemphasis applied to the data before
quantization.
The only emphasis value defined here is
emphasis=50-15 to indicate 50/15 microsecond preemphasis.
parameter MUST be omitted if no analog preemphasis was applied.
channel-order: specifies the sample interleaving order for
multiple-channel audio streams (see RFC 3190 Section 7).
Permissible values are DV.LRLsRs, DV.LRCS, DV.LRCWo,
DV.LRLsRsC, DV.LRLsRsCS, DV.LmixRmixTWoQ1Q2,
DV.LRCWoLsRsLmixRmix, DV.LRCWoLs1Rs1Ls2Rs2, DV.LRCWoLsRsLcRc.
For interoperation with DV video systems, none of these channel
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combinations is specified for use with 20-bit linear encoding
in the DV video specification [4]; only mono and stereo are
This parameter MUST be omitted when the AIFF-C
channel order convention is in use.
Encoding considerations:
L20 audio can be transmitted with RTP as specified in RFC 3190.
Security considerations: See Section 9.
Interoperability considerations: NONE
Published specification:
Applications which use this media type:
Audio communication.
Additional information:
Magic number(s): None
File extension(s): None
Macintosh File Type Code(s): None
Person & email address to contact for further information:
Katsushi Kobayashi
e-mail: ikob@koganei.wide.ad.jp
Intended usage: COMMON
Author/Change controller:
Katsushi Kobayashi
e-mail: ikob@koganei.wide.ad.jp
8.3 MIME registration form for audio/L24
MIME media type name: audio
MIME subtype name: L24
Required parameters:
rate: number of samples per second -- RECOMMENDED values for rate
are , 1, 2, 44100 and 48000
samples per second.
Other values are permissible.
Optional parameters:
channels: how many audio streams are interleaved -- defaults to 1;
stereo would be 2, etc.
Interleaving takes place between
individual 24-bit samples.
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emphasis: analog preemphasis applied to the data before
quantization.
The only emphasis value defined here is
emphasis=50-15 to indicate 50/15 microsecond preemphasis.
parameter MUST be omitted if no analog preemphasis was applied.
channel-order: specifies the sample interleaving order for
multiple-channel audio streams (see Section 7).
Permissible
values are DV.LRLsRs, DV.LRCS, DV.LRCWo, DV.LRLsRsC,
DV.LRLsRsCS, DV.LmixRmixTWoQ1Q2, DV.LRCWoLsRsLmixRmix,
DV.LRCWoLs1Rs1Ls2Rs2, DV.LRCWoLsRsLcRc.
This parameter MUST be
omitted when the AIFF-C channel order convention is in use.
Encoding considerations:
L24 audio can be transmitted with RTP as specified in RFC 3190.
Security considerations: See Section 9.
Interoperability considerations: NONE
Published specification:
Applications which use this media type:
Audio communication.
Additional information:
Magic number(s): None
File extension(s): None
Macintosh File Type Code(s): None
Person & email address to contact for further information:
Katsushi Kobayashi
e-mail: ikob@koganei.wide.ad.jp
Intended usage: COMMON
Author/Change controller:
Katsushi Kobayashi
e-mail: ikob@koganei.wide.ad.jp
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Security Considerations
RTP packets using the payload format defined in this specification
are subject to the security considerations discussed in the RTP
specification [1], and any appropriate RTP profile [2].
This implies
that confidentiality of the media streams is achieved by encryption.
Because the data compression used along with this payload format is
applied end-to-end, encryption may be performed after compression so
there is no conflict between the two operations.
A potential denial-of-service threat exists for data encodings using
compression techniques that have non-uniform receiver-end
computational load.
The attacker can inject pathological datagrams
into the stream which are complex to decode and cause the receiver to
be overloaded.
However, this encoding does not exhibit any
significant non-uniformity.
As with any IP-based protocol, in some circumstances a receiver may
be overloaded simply by the receipt of too many packets, either
desired or undesired.
Network-layer authentication may be used to
discard packets from undesired sources, but the processing cost of
the authentication itself may be too high.
In a multicast
environment, pruning of specific sources may be implemented in future
versions of IGMP [9] and in multicast routing protocols to allow a
receiver to select which sources are allowed to reach it.
IANA Considerations
This document defines two new MIME subtype-specific optional
parameters "emphasis" and "channel-order", which are specified with
the sets of permissible values for those parameters in Sections 5 and
7, respectively.
Section 8 includes registrations for three new MIME
subtypes that use those optional parameters.
These registrations
define the subset of the optional parameter values allowed for each
It is expected that the number of additional values that
will need to be defined for these optional parameters is small.
Therefore, anyone wishing to define new values is required to produce
a revision of this document to be vetted through the normal Internet
Standards process.
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References
[1] Schulzrinne, H., Casner, S., Frederick, R. and V. Jacobson, "RTP:
A Transport Protocol for real-time applications," RFC 1889,
January 1996.
[2] H. Schulzrinne, "RTP profile for audio and video conferences with
minimal control", RFC 1890, January 1996.
[3] IEC 61119, Digital audio tape cassette system (DAT), November
[4] IEC 61834, Helical-scan digital video cassette recording system
using 6,35 mm magnetic tape for consumer use (525-60, 625-50,
1125-60 and 1250-50 systems), August 1998.
[5] Salsman, J., "The Audio/L16 MIME content type", RFC 2586, May
[6] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[7] Handley, M. and V. Jacobson, "SDP: Session Description Protocol",
RFC 2327, April 1998.
[8] Kobayashi, K., Ogawa, A., Casner, S. and C. Bormann, "RTP Payload
Format for DV (IEC 61834) Video", RFC 3189, January 2002.
[9] Deering, S., "Host Extensions for IP Multicasting", STD 5, RFC
1112, August 1989.
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The DV audio channel symbols are specified in Table 2.
These symbols
are taken from the notation used in the DV video specification IEC
], chapter 8.1.
For the exact meaning of each symbol, the
original DV video specification should be consulted.
L: Left channel of stereo
R: Right channel of stereo
M: Monaural signal
C: Center channel of 3,4,6 or 8 channel audio
S: Surround channel of 4 channel audio
Ls, Ls1, Ls2: Left surround channel
Rs, Rs1, Rs2: Right surround channel
Lc: Left center channel of 8 channel audio
Rc: Right center channel of 8 channel audio
Wo: Woofer channel
Lmix: L + 0.7071C + 0.7071LS
Rmix: R + 0.7071C + 0.7071RS
T: 0.7071C
Q1: 0.7071LS + 0.7071RS
Q2: 0.7071LS - 0.7071RS
Table 2. Channel symbols for audio channels in DV video [4]
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Authors' Addresses
Katsushi Kobayashi
Communication Research Laboratory
4-2-1 Nukii-kita machi, Koganei
Tokyo 184-8795 JAPAN
Phone: +81 42 327 6174
EMail: ikob@koganei.wide.ad.jp
Akimichi Ogawa
Keio University
5322 Endo, Fujisawa
Kanagawa 252 JAPAN
akimichi@sfc.wide.ad.jp
Stephen L. Casner
Packet Design
2465 Latham Street
Mountain View, CA 94040
United States
Phone: +1 650-943-1843
EMail: casner@acm.org
Carsten Bormann
Universitaet Bremen TZI
Postfach 330440
D-28334 Bremen, Germany
Phone: +49 421 218 7024
+49 421 218 7000
EMail: cabo@tzi.org
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Full Copyright Statement
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Acknowledgement
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Internet Society.
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