Hydrogenaudio Knowledgebase - User contributions [en]

Talk:LAME

2013-05-10T20:11:13Z

79.133.131.255:

{{talkheader}}

==Page discussion==
I propose a major merging with this page. I don't think information about lame should be scattered all over the wiki. I'll think about it this evening and after the merge I'll add a redirect from all Lame related pages to this one.--[[User:Beto|Beto]] 15:51, 13 September 2006 (CDT)

Finally I ended the revision :)--[[User:Beto|Beto]] 19:14, 14 September 2006 (CDT)

== LAME compiles Win32 ==

http://rarewares.org/dancer/dancer.php?f=1 is linked at this Wiki page. But at http://rarewares.org/mp3.html I can only find http://rarewares.org/dancer/dancer.php?f=107 The two archives contain different lame.exe and lame_enc.dll. Why is that? Here's another compile: http://mitiok.maresweb.org/ This is confusing! --[[User:Pohli|Pohli]] 13:16, 27 September 2006 (CDT)

:IMO we should '''not''' give direct link to the downloader; everytime a new build is outed, the direct link becomes outdated. Better to link only to Rareware's MP3 page. --[[User:Pepoluan|pepoluan]] '''([[User_talk:pepoluan|talk]] | [[Special:Contributions/pepoluan|contribs]])''' 13:46, 27 September 2006 (CDT)
:Agree. If noone oposes we should make the change.--[[User:Beto|Beto]] '''([[User_talk:Beto|talk]] | [[Special:Contributions/Beto|contribs]])''' 15:48, 27 September 2006 (CDT)
:PLUS, LAME binaries are illegal in many countries. It's easy to use google. {{User:Elliottmobile/sig2}} 02:10, 28 September 2006 (CDT)

==Define quality==

Much is made of LAME's "quality" settings, but this term is not really defined. I believe the main definition of quality is inverse of quantization noise (more noise = lower quality). Are there other factors? And it'd be worth remarking on how higher quality is often achieved: by using higher bitrates, using different psychoacoustic models, or simply chopping off the high end.

There is also no mention of the tuning that has been done for LAME's presets and default settings at certain bitrates. Much attention has been given to optimizing VBR, ABR, and the common (128 kbps and up) bitrates, but not so much for the CBR lower bitrates. For example, as I mentioned at the bottom of the [[CBR]] article, a certain other codec's default setting for 96 kbps CBR stereo output uses about an 11.5 kHz lowpass filter on the input, as compared to LAME which defaults to about a 12.5 kHz filter. LAME allows for more high end in the audio, but encodes it with more noise (bleepy artifacts), too. For some, it's an even trade, and LAME's definition of "quality" is equivalent to that of the other encoder. But for others, one encoder or the other produces qualitatively inferior output. In other words, each encoder has its own definition of ''measurable'' quality, and its own standard of quality for its presets, and each listener has his/her own subjective tolerances and criteria for ''perceived'' quality. So this is why I'd like to see an explanation of exactly which factors are used in LAME's quality settings. -- [[User:Mjb|Mjb]] 04:10, 19 January 2008 (CST)

== My usual (best) settings: ==
lame version 3.93.1 - only this version work ok for -k.
lame.exe -q0 -k --vbr-new -v -V3 -b32 -B256 my.wav

Talk:LAME

2013-05-10T20:06:43Z

79.133.131.255: /* My usual (best) settings: */ new section

Channel coupling

2013-05-10T19:59:28Z

79.133.131.255: /* Vorbis Channel Coupling */ dual stereo - will be quadro :)

'''Channel coupling''' is a method used to reduce [[bitrate]] demand by coding the stereo channel information more efficiently. there are several channel coupling methods. In [[MP3]] the general term is [[joint stereo]].

== MP3 Channel Coupling ==
MP3 can use 2 different channel coupling methods: mid/side-coding and [[intensity stereo]]. Mid/Side-coding calculates a "mid"-channel by addition of left and right channel (l+r)/2 and a "side"-channel (l-r)/2. With more mono-like signals one can use less [[bitrate]] to encode the side-channel, so that the overall bitrate will be less than encoding the left and right channel. Intensity stereo destroys phase information, so it's used only at low bitrates.

Correctly implemented MP3 mid/side stereo (like in [[LAME]]) does very little or no damage to the stereo-image and increases compression efficiency either by reducing size or increasing overall quality.

== Vorbis Channel Coupling ==
(Ogg) [[Vorbis]] treats stereo information with '''square polar mapping''' which is beneficial when the correlation between the left and right channels are strong (this can also be extended to multichannel coupling as well). In Vorbis, the spectrum of each channel is normalized against a floor function, which is a rough envelope of the actual spectrum. In the square polar mapping, the (stereo) phase is roughly defined as the difference between the normalized left and right amplitude of a given frequency component. If the original left and right channel are the same within a certain frequency band, apart from an overall scaling factor, then the normalized frequency spectrum is the same left and right and the stereo phase is zero over the whole frequency band. Note that in the context of polar mapping, the term 'phase' (here: 'stereo phase') has a very different meaning from the phase of a periodic wave. Unlike in the Fourier Transform, the Cosine Transform used in Vorbis and other encoders only provides amplitudes and no phases of the latter type.

Once the stereo information is represented in polar mapping as a magnitude and stereo phase, Vorbis can use three coupling methods:
* '''Lossless coupling''' is equivalent to independent encoding of the two channels ('dual mono' in MP3), but with the benefit of additional space-saving. It does polar mapping/channel interleaving using the residue vectors.
* In [[point stereo]], the stereo phase is discarded completely. All the stereo information comes from the difference in the spectral floors for the left and right channels.
* In '''phase stereo'''', the stereo phase is quantized, i.e. stored at a lower resolution. Especially above 4 kHz, the ear is not very sensitive to phase information. Phase stereo is '''not''' currently implemented in reference encoder due to complexity, but will be re-added again later on. Note that phase stereo should not be compared to intensity stereo in MP3 coding.

Ogg Vorbis uses lossless/point stereo coupling below ''-q 6''. Lossless channel coupling is used for high bitrates entirely (''-q 6 and up''). This can be adjusted via an advanced-encode switch, but is not done for simplicity's sake.

=== Additional Reading ===
* [http://www.xiph.org/vorbis/doc/stereo.html Ogg Vorbis stereo-specific channel coupling] at xiph.org.

[[Category:Technical]]

Joint stereo

2013-05-10T19:49:40Z

79.133.131.255:

'''Joint stereo''' is a property of an audio data stream and means that the stream supports more than one method of stereo coding, such as SS ("simple" or "L/R" stereo or DualMono), MS ("mid-side" stereo), or IS ("intensity" stereo). A joint stereo stream may still only employ a single coding method, but for the sake of efficiency or quality may switch between methods on a frame or even sub-frame basis.

For example, a high-[[bitrate]] "joint stereo" [[MP3]] file may contain a mixture of SS and MS frames, or it may contain all SS frames or all MS frames. A non-"joint stereo" MP3 will never contain a mixture of frame types.

"Joint stereo coding methods" in prose generally refers to whatever alternatives to simple (L/R) stereo coding are supported by a particular format, even though simple stereo is also an option.

==Stereo coding methods or "modes"==

===Left-Right (L/R) or "Simple" Stereo (SS)===
Simple stereo is the most straightforward method of coding a stereo signal: each channel is treated as a completely separate entity. This can be inefficient and may adversely impact quality (as compared to other modes) when both channels contain nearly identical signals (i.e., are mono or nearly so).

===Mid-side Stereo (MS)===
Mid-side stereo coding calculates a "mid"-channel by addition of left and right channel, and a "side"-channel, i.e.:

<center><math>Left = L \qquad Right = R\,</math></center>

<center><math>Middle=\frac{L+R}{2} \qquad Side=\frac{L-R}{2}</math></center>

<center> <math>Left=Middle+Side \qquad Right=Middle-Side</math></center>

Whenever a signal is concentrated in the middle of the stereo image (i.e. more mono-like), mid-side stereo can achieve a significant saving in bitrate, since one can use fewer bits to encode the side-channel. Even more important is the fact that by applying the inverse matrix in the decoder, the quantization noise becomes correlated and falls in the middle of the stereo image, where it is masked by the signal.

Unlike [[Joint stereo#intensity stereo|intensity stereo]] which destroys phase information, mid-side coding keeps the phase information pretty much intact. Correctly implemented mid-side stereo does very little or no damage to the stereo image and increases compression efficiency either by reducing size or increasing overall quality.

===Intensity Stereo===

Intensity stereo coding is a method that achieves a saving in bitrate by replacing the left and the right signal by a single representing signal plus directional information. This replacement is psychoacoustically justified in the higher [[frequency]] range since the human auditory system is insensitive to the signal phase at frequencies above approximately 2kHz.

Intensity stereo is by definition a [[lossy]] coding method thus it is primarily useful at low bitrates. For coding at higher bitrates only mid-side stereo should be used.

==Additional information==

Some early MP3 encoders didn't make ideal decisions about what mode to use from frame to frame in joint stereo files, or how much bandwidth to allocate to encoding the side channel. This led to a widespread but mistaken belief that an abundance of M/S frames, or the use of joint stereo in general, always negatively impacts channel separation and other measures of audio quality. This is not an issue with modern encoders. Modern, optimized encoders will switch between mid-side coding or simple stereo coding as necessary, depending on the correlation between the left and right channels, and will allocate channel bandwidth appropriately to ensure the best mode is used for each frame.

==External Links==
* <s>[http://harmsy.freeuk.com/mostync/ Joint stereo myths and realities]</s> ''(very important read, but fails to observe that a "joint stereo" file may very well contain 100% simple stereo data!)''

* [http://www.audiocoding.com/ Audiocoding] -- written by Menno Bakker

* [http://www.High-Quality.ch.vu/ High Quality Audio guides] -- written by user Note: Recommendation of MPC is his preference.

* [http://en.wikipedia.org/wiki/Joint_stereo joint stereo at wikipedia]

[[Category:Technical]]