LAME

LAME is an open source project, which sees itself as a development project to support the MP3 technology. The name LAME is a recursive acronym for LAME Is not an MP3 Encoder, " LAME is not an MP3 Encoder", which is due to the fact that LAME was originally not a complete encoder, but only a patch for the MP3 sample implementation, see History. De facto developed the LAME project source for the generation of MP3 audio files and is therefore in competition with other providers, such as the Fraunhofer Society (FhG) with their licensed MP3 encoders. LAME is used in a variety of free software products and, according to the LAME project in at least one portable MP3 player. LAME is licensed under the GNU Lesser General Public License ( LGPL) and can therefore be used freely.

• 4.2.1 mono
• 4.2.2 Joint - Stereo
• 4.2.3 Simple Stereo
• 4.2.4 Dual-Mono/Dual-Channel

• 5.1 Setting Profiles
• 5.2 Quality Levels

History

The project started in early 1998 when Mike Cheng developed a patch for an example implementation of an MP3 encoder. This encoder was published by the International Organization for Standardization ( ISO) and may be used freely for non-commercial projects. The ISO manages all MPEG standards (and thus also MP3), but that only affects the format itself and the decoding, which are freely available as an ISO standard, not the coding. LAME is licensed under the LGPL and comes in version 3.81beta of 8 May 2000 without the old ISO code. LAME is widely regarded as the highest quality MP3 encoder, which is concluded from numerous listening tests. He is also one of the fastest By constant optimizations. The LAME MT project is working on a version with multi-threaded engine to make use of multi-core processors better use.

Licenses and Patents

The Fraunhofer-Gesellschaft and other companies have software patents on partial methods that are used for MPEG encoding. An all-encompassing MP3 patent does not exist. The Fraunhofer-Gesellschaft has contributed the major part in the development of the MP3 standard and can be patented, some methods for MP3 encoding. In a merger with Thomson they both own 18 MP3 - related patents. Since September of 1998, when the MP3 standard was six years establish unloaded, requires FhG / Thomson royalties for MP3 encoder. Other companies also have claims on the MP3 process, for example, the company Sisvel, who acts on behalf of Philips.

As a result, many free MP3 projects had to be abandoned. The claim of FhG / Thomson, that the use of their patents for MP3 encoding would be indispensable, could be enforced against LAME been judicially not. The LAME developers could rely on it to use the freely available ISO Source under the appropriate license to be a MP3 technology - supportive development project and to offer not a finished product, but only to publish the source code. This means that those who LAME -based encoders provide, also received a degree of risk by spreading a finished product. FhG / Thomson would, however, first to demonstrate the validity and applicability of its patents.

Use

Due to the high quality of the generated LAME MP3 files, it is widely used and is often found in shareware and freeware programs. On Windows, some encoder programs need (such as VirtualDub ) in addition to a codec Audio Compression Manager (ACM ) for LAME (see links).

In November 2005, there were reports that analyzes pointed out that that was unlawfully used in the controversial XCP copy protection method, which was used on music CDs from Sony BMG, source of LAME. As Sony finally withdrew all CDs with XCP, however, these allegations went to nothing.

Supported techniques

Bit rate modes

Constant data rate (CBR)

Constant bit rate can be selected from 32, 40, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, and 320 kbit / s Here the quality is variable.

Variable data rate ( VBR)

Variable bit rate in ten quality levels (-V 0 to V - 9). By dynamically adjusting the bit rate to the complexity of the audio signal is attempted to keep the quality constant. In connection with VBR is often spoken of a nominal (ie, average ) bit rate. With Lame 3.90 Alt presets have been introduced that provide a transparent quality.

Average Data Rate (ABR )

LAME also supports setting an average data rate. On the technical side, although it is the same as variable data rate, however, is here from the encoder tries to reach the given bit rate average. However, the achieved bit rate generally differs minimally from the target result from ( For example, if 192 kbit / s, which are entered as target bit rate, the bandwidth of the bit rate, which is achieved, 180-200 kbit / s ). So it is a mixture of technique of VBR with the idea of CBR.

Channel modes

Mono

If the source file is not monophonic, it is converted to mono ( a so-called down-mix) and encoded in MP3. It is used only one audio channel.

Joint stereo

A distinction is made between the lossy IS- joint stereo, lost in the phase information, and lossless MS joint stereo. The current version of the LAME encoder used by the lowering of the target bit rate independent, only MS joint stereo.

Mid / side joint stereo uses the fact that there are at normal music between the two stereo channels only small differences. The two channels are added to a sum channel L R ( "MID" ), which is the left and right channel jointly grouped (English joint " connected "). The second channel contains only the difference signal LR ( "Side "), which is generally much less complex. Low frequencies are not differentiated because their direction information is negligible. In this manner, a much higher quality can be achieved with identical bit rate compared to the conventional stereo method. For audio sources that contain completely separate images for the left and right channels, but this method is not profitable because of Points with large channel differences automatically simple stereo is used ( this function is deactivated in the channel mode Forced Joint Stereo; are here all frames with MS joint stereo processed).

Simple stereo

There are two independent audio channels stored. Depending on the complexity assigned to the two channels corresponding bit rates, the left channel for example, 65 % of the space and the right 35%. The quality is due to joint stereo ( with normal stereo files, the same bit rate and the same memory space ) consequently worse.

Dual-Mono/Dual-Channel

As with simple stereo both channels are encoded separately. The difference is that, get half the storage space regardless of the complexity of the right or left channel, both channels exactly. This result is thus reached with simple stereo.

Coding speed

LAME was and is not the fastest MP3 encoder. Also LAME encoder is slower than other compression methods generally. The reasons for this are, for example, in the psycho- acoustic model and other internal functions, which serve to improve the output quality. Thus, the slow processing directly benefits the quality. In the calculation speed of modern computers, however, the waiting times are less and less significant.

Others

• The quality and speed of the encoding can be influenced.
• The low-pass filtering is enabled by default, but can also be disabled.
• ID3v1 and ID3v2 tagging.
• Replay Gain (enabled by default ).
• CRC calculation of the header.
• Gapless ( continuous free ) encoding.
• Input ( source files ) can be both WAV and MP1, MP2 and MP3 files.
• MP3 files can be converted to wav files ( Decode ).
• Free format bitstreams ( which do not correspond to the bit rate 32, 40, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256 or 320 kbit / s) can be generated.

LAME allows for many more settings for MP3 encoding, either directly via the command line or via the user interface of a supporting software.

It is recommended to use VBR encoding. This ensures that the piece of music is encoded with a constant quality. In contrast, the quality varies with the coding with a constant data rate, this reduction in quality can be difficult to be encoded music spots occur. VBR encoding reduces the data rate at the quieter passages of the piece and lifts it in complex passages. This ensures a constant quality is achieved and there is a minimum necessary for file size.

To encode with LAME variable bitrate, in addition to the conventional VBR mode is also the new VBR mode. Since he is very mature since version 3.97, and the encoding speed has tripled, it should be used by default, which in Lame automatically from version 3.98 is the case.

Setting profiles

Because of the large flexibility of the LAME encoding capability using many parameters can be controlled very accurately. However, since these many ways, because of their complexity lead to non-optimal results, it is a system of preference profiles (English presets = preset ).

Three stages are given, which provide optimal solutions to everyday use. The Standard level (equivalent to - V 2) generates a transparent quality, in most people's MP3 -encoded version sound can not distinguish from the original. Therefore, it is the recommended setting for encoding music. The underlying medium level (equivalent to V - 4) is a good compromise between small file size and adequate quality dar. Since it produces almost transparent quality, it is well suited to prepare music for portable mp3 players. The Extreme Stage (equivalent to - V 0) brings over the standard level only small improvements in quality, but leads to very large files.

The presets can for example - preset standard activated. Also as presets the quality levels ( see next section) can be viewed. So who wants to work for better gradation directly with these parameters, which can do this by using, for example, V - 2 as a parameter.

Quality levels

LAME has been improved in quality in recent years. According to recent listening tests, that most people with LAME music encoded at an average bit rate of 128 kbit / s perceive as transparent. Thus LAME now reached at this bit rate (as of September 2007), a quality that was not possible with the introduction of the MP3 format. Therefore, the following assessment for the LAME encoder is valid only on version 3.97. Only a few pieces of music contain short passages ( problem samples) that do not sound transparent even at high quality settings. In normal music enjoyment but are not to hear even these differences. The following table is for guidance on the 10-step quality levels system.

Of course, the values ​​shown here are only indicative, because depending on the starting material, the bit rate can also significantly example at quality level V - 2 below 170 kbit / s or 210 kbit / s. Since the version 3.98 and non- integer values ​​are accepted as parameters for V.

Hearing tests

Audio codecs were repeatedly subjected to various hearing tests (for example ABX test). Thus, it is possible to " tune" to a codec, in response to the result. The Community on Hydrogenaudio.org tested Lame Encoder and other regular hearing tests. The results were incorporated directly into the development of Lame, so that the encoder could be continuously improved. As an example, the coding quality at 128 kbit / s named in which Lame could improve steadily. So Lame reached in version 3.95 in a test 3.74 points, the next version Lame 3.96 in another test already 4.18 points and Lame 3.97b2, again in another test 4.60 of 5 points each. However, participated in the listening tests in part different individuals and some other test data were used. Thus, the results can not be applied directly to each other, but still offer an insight into the development of the codec, which could increase tends to significantly in quality. Was it in 2002 at 128 kbit / s only speak of sufficient quality, so 2007 is the quality most listeners already transparent.