Editing Stereophonic sound (section)

==Recording methods==
{{see also|Microphone practice#Stereo recording techniques}}

===A-B technique: time-of-arrival stereophony===
[[File:AB Stereo.svg|thumb|A-B stereo microphone placement]]
The A-B technique uses two omnidirectional microphones some distance apart and equidistant from the source. The technique captures time-of-arrival stereo information as well as some level difference information{{snd}}especially if employed in close proximity to the source. At a distance of about {{convert|60|cm|in|abbr=on}} between microphones, the time-of-arrival difference for a signal reaching the first microphone and then the other one from the side is approximately 1.75&nbsp;ms. If you increase the distance between the microphones, you effectively decrease the pickup angle. At a {{convert|70|cm|in|abbr=on}} distance, it is approximately equivalent to the pickup angle of the near-coincident [[ORTF stereo technique|ORTF]] setup.{{cn|reason=need a definition for ''pickup angle''|date=May 2025}}

This technique can produce phase issues when the stereo signal is mixed to mono.<!--[[User:Kvng/RTH]]-->

===X-Y technique: intensity stereophony===
[[File:XY stereo.svg|thumb|X-Y stereo microphone placement]]
Here, two directional [[microphone]]s are at the same place, typically pointing at an angle between 90° and 135° to each other.<ref>{{cite web |url=http://www.rycote.com/images/uploads/The_Stereophonic_Zoom.pdf |archive-url=https://web.archive.org/web/20110531142452/http://www.rycote.com/images/uploads/The_Stereophonic_Zoom.pdf |url-status=dead |archive-date=May 31, 2011 |title="The Stereophonic Zoom" by Michael Williams |access-date=October 17, 2011 |df=mdy-all }}</ref> The stereo effect is achieved through differences in sound pressure level between two microphones. A difference in levels of 18&nbsp;dB (16 to 20&nbsp;dB) is needed for hearing the direction of a loudspeaker. Due to the lack of differences in time-of-arrival/phase ambiguities, the sonic characteristic of X-Y recordings has less sense of space and depth when compared to recordings employing an A-B setup. When two figure-eight microphones are used, facing ±45° with respect to the sound source, the X-Y setup is called a [[Blumlein pair]]. The sonic image produced is realistic.

===M/S technique: mid/side stereophony===
[[File:MS stereo.svg|thumb|Mid/side stereo microphone technique]]
This coincident technique employs a bidirectional microphone facing sideways and another microphone at an angle of 90°, facing the sound source. The second microphone is generally a variety of cardioid, although [[Alan Blumlein]] described the usage of an omnidirectional transducer in his original patent.

The left and right channels are produced through a simple matrix: left = mid + side; right = mid − side (the polarity-reversed side signal). This configuration produces a completely mono-compatible signal and, if the mid and side signals are recorded (rather than the matrixed left and right), the stereo width can be manipulated after the recording has taken place. This makes it especially useful for film-based projects.

===Near-coincident technique: mixed stereophony===
[[File:ORTF-Stereo.svg|thumb|left| [[ORTF]] stereo microphone technique]]
These techniques combine the principles of both [[AB Class amplifier|A-B]] and [[X-Y]] ([[coincident pair]]) techniques. For example, the [[ORTF stereo technique]] of the [[Office de Radiodiffusion Télévision Française]] ([[Radio France]]) calls for a pair of [[cardioid microphone]]s placed 17&nbsp;cm apart at a total angle between microphones of 110°, which results in a stereophonic pickup angle of 96° (''[[Stereo Recording Angle]]'', or SRA).<ref>{{cite web |author=Eberhard Sengpiel |url=http://www.sengpielaudio.com/ |title=Forum für Mikrofonaufnahme und Tonstudiotechnik. Eberhard Sengpiel |publisher=Sengpielaudio.com |access-date=October 17, 2011 |archive-date=October 17, 2011 |archive-url=https://web.archive.org/web/20111017211953/http://www.sengpielaudio.com/ |url-status=live }}</ref> In the [[NOS stereo technique]] of the Nederlandse Omroep Stichting (Dutch Broadcasting Organisation), the total angle between microphones is 90° and the distance is 30&nbsp;cm, thus capturing time-of-arrival stereo information as well as level information. It is noteworthy that all spaced microphone arrays and all near-coincident techniques use a spacing of at least 17&nbsp;cm or more. 17&nbsp;cm roughly equals the human ear distance and therefore provides the same interaural time difference (ITD) or more, depending on the spacing between microphones. Although the recorded signals are generally intended for playback over stereo loudspeakers, reproduction over headphones can provide remarkably good results, depending on the microphone arrangement.

===Pseudo-stereo===
[[File:stereo_widening_example.svg|thumb|192px|A stereo-widening example:<ref>Rick Snoman, [http://google.com/books/edition/Dance_Music_Manual/GRdmAQAAQBAJ ''Dance Music Manual &ndash; Tools, Toys, and Techniques''], 15 October 2013, {{ISBN|9781135964092}}</ref>
{|
|valign="top"|{{nowrap|1.}}||A is a square wave and B is one thrice the frequency.
|-
|valign="top"|2.||Different amounts of A and B are mixed into the {{nowrap|left (L)}} and {{nowrap|right (R)}} channels.
|-
|valign="top"|3.||To widen the stereo effect, a fraction of the opposing channel is subtracted from each channel.
|-
|valign="top"|4.||Normalised results show the signals A and B partly separated.
|}]]
In the course of restoration or remastering of [[monaural|monophonic]] records, various techniques of ''pseudo-stereo'', ''quasi-stereo'', or ''rechanneled stereo'' have been used to create the impression that the sound was originally recorded in stereo. These techniques first involved hardware methods (see [[Duophonic]]) or, more recently, a combination of hardware and software. Multitrack Studio, from Bremmers Audio Design (The Netherlands),<ref>{{cite web |url=http://www.multitrackstudio.com/pseudostereo.php |title=Pseudo-Stereo |publisher=Multitrackstudio.com |access-date=October 17, 2011 |archive-date=October 4, 2011 |archive-url=https://web.archive.org/web/20111004035631/http://www.multitrackstudio.com/pseudostereo.php |url-status=live }}</ref> uses special filters to achieve a pseudo-stereo effect: the ''shelve'' filter directs low frequencies to the left channel and high frequencies to the right channel, and the [[comb filter]] adds a small delay in signal timing between the two channels, a delay barely noticeable by ear,<ref group=note>The comb filter allows range of manipulation between 0 and 100 [[milliseconds]].</ref> but contributing to an effect of ''widening'' original ''flattiness'' of mono recording.<ref>{{Cite web|date=March 31, 2008|title=Hyperprism-DX Stereo Processes—Quasi stereo<!--|chapter=Quasi stereo-->|url=http://ecmc.rochester.edu/ecmc/docs/hyperprism1.5.5/stereo.HTM|archive-url=https://web.archive.org/web/20080331024716/http://ecmc.rochester.edu/ecmc/docs/hyperprism1.5.5/stereo.htm|archive-date=2008-03-31}}</ref><ref>[http://cec.concordia.ca/econtact/8_3/gauthier.html A Review and an Extension of Pseudo-Stereo...] {{webarchive |url=https://web.archive.org/web/20071206065506/http://cec.concordia.ca/econtact/8_3/gauthier.html |date=December 6, 2007 }}</ref>

The special pseudo-stereo circuit{{snd}} invented by Kishii and Noro, from Japan{{snd}} was patented in the United States in 2003,<ref>{{cite web |url=http://www.freepatentsonline.com/6636608.html |title=Pseudo-stereo circuit—Patent 6636608 |publisher=Freepatentsonline.com |date=October 21, 2003 |access-date=October 17, 2011 |archive-date=June 15, 2011 |archive-url=https://web.archive.org/web/20110615003238/http://www.freepatentsonline.com/6636608.html |url-status=live }}</ref> with already previously issued patents for similar devices.<ref>{{cite web |url=http://www.patentstorm.us/patents/5355416/description.html |archive-url=https://web.archive.org/web/20081204103229/http://www.patentstorm.us/patents/5355416/description.html |url-status=dead |archive-date=December 4, 2008 |title=Psycho acoustic pseudo-stereo fold system |publisher=Patentstorm.us |access-date=October 17, 2011 |df=mdy-all }}</ref> Artificial stereo techniques have been used to improve the listening experience of monophonic recordings or to make them more "saleable" in today's market, where people expect stereo. Some critics have expressed concern about the use of these methods.<ref>{{cite magazine|url=http://www.time.com/time/magazine/article/0,9171,871986,00.html |archive-url=https://web.archive.org/web/20080308123110/http://www.time.com/time/magazine/article/0,9171,871986,00.html |url-status=dead |archive-date=March 8, 2008 |title=''Pseudo Stereo'', Time magazine, Jan.&nbsp;20,&nbsp;1961 |magazine=Time  |date=January 20, 1961 |access-date=October 17, 2011}}</ref>