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Chapter 8: Multimiking In Stereo

AUDIO FILES (To download all WAV examples at once: 23MB ZIP)

  • Dry/Wet Ratio & Tone Of Central Sources For Different XY Mutual Angles: For the following three audio examples I replayed a small snippet of the BBC shipping forecast through a loudspeaker at the centre of the soundstage, and recorded it in stereo with three different crossed cardioid pairs. The microphones were all Avantone CK1 small-diaphragm condenser mics, so the only variable in these tests was the mutual angle between the mics in each case: 90 degrees (Ex08.01:WAV/MP3
    )
    ; 110 degrees (Ex08.02:WAV/MP3
    )
    , and 140 degrees (Ex08.03:WAV/MP3
    )
    respectively -- figures that will be familiar to anyone who's perused Tables 8.1 and 8.3 in the book! There are two specific things to notice: firstly, that the relative dry level of the centrally located source reduces as the mutual angle increases, making it appear more distant; and secondly that the tone of the voice becomes noticeably duller with increasing mutual angle, on account of the source moving progressively further off-axis to the mics.

  • AB Stereo Miking Comparisons: With spaced stereo techniques, the spacing between the mics determines the array's acceptance angle, and hence the apparent stereo spread of the captured instrument, as you can hear by comparing these AB classical-style recordings of a grand piano taken from in front of the instrument, with the mics positioned just below the angle of the open lid at a distance of around 2.2m. In the first excerpt (Ex08.05:WAV/MP3
    )
    , the small-diaphragm microphones were only spaced roughly 40cm apart, whereas in the second snippet (Ex08.06:WAV/MP3
    )
    the distance between them was more like a metre. It's also interesting to compare the sound of the wider-spaced pair when its omni capsules are replaced with cardioids (Ex08.07:WAV/MP3
    )
    -- notice that the presentation is considerably drier and more restricted at the low end of the spectrum, as you'd expect, but that the stereo imaging is nonetheless very comparable.

  • Coincident, Spaced, & Near-coincident Stereo Techniques Compared: The following examples provide a demonstration of the relative characteristics of coincident, spaced, and near-coincident stereo recording methods. The setups on trial are a cardioid XY setup with a 110-degree mutual angle (Ex08.10:WAV/MP3
    )
    ; an omni AB setup with a 100cm inter-mic spacing (Ex08.11:WAV/MP3
    )
    ; and an ORTF near-coincident setup with a mutual angle of 110 degrees and a 17cm inter-mic spacing (Ex08.12:WAV/MP3
    )
    . Whether the near-coincident setup combines the advantages or disadvantages of the XY and AB rigs is one of those judgement calls every engineer has to make...

LINKS

  • Printable Stereo Protractor: Here's a PDF document you can print out to help you setting up stereo-pair mutual angles more accurately. For reference, I've also indicated on it the suggested mutual angles given in Table 8.1 of the book.

  • Origami Mutual-angle & Mic-spacing Templates: It's possible to fold a mutual-angle template for any angle up to 160 degrees (increments of 5 degrees, accuracy +/-1 degree) from a piece of A4 paper -- this PDF document shows you how. Note that, although I've included the ‑30/‑60 and ‑20/‑70 folds for the sake of completeness, I rarely bother with them -- the ‑35, ‑45, and ‑55 folds on their own already allow angle templates for 70, 80, 90, 100, 110, 125, 135, and 145 degrees (as well as various smaller angles by halving), which gets you within 5 degrees of any of the suggested mutual angles in Table 8.1. Origami mic-spacing templates are also easy to create, given that A4 paper measures roughly 20cmx30cm, and these dimensions are easily halved/quartered to 5cm, 10cm, and 15cm.

  • Affordable Stereo Bars: The K&M 23550 and 23510 short stereo bars are both affordable and good-quality, but if you're after something longer and more elaborate (with mutual-angle and spacing markers), check out Superlux's relatively affordable MA90.

  • Low-frequency Shuffling Implementations: There are several ways to implement the low-frequency shuffling technique mentioned in the book, the simplest being to use one of those increasingly common MS-enabled EQ plug-ins to dial in 3-6dB of low-frequency shelving boost in the sub-500Hz region of the Sides channel. However, if you're trying to implement this kind of processing from first principles, this PDF document gives a couple of block diagrams of specific implementations to get you started.

  • Freeware MS-Encoder/Decoder & Vectorscope Plug-ins: For MS encoding and decoding (as well as simple MS rebalancing) in a software DAW, you need look no further than Voxengo's excellent cross-platform freeware MSEDMac LogoWindows Logo plug-in -- a utility that I use on a daily basis. There's also a couple of great cross-platform freeware vectorscope plug-ins available if you're struggling to judge stereo width over headphones or under compromised monitoring conditions: Flux's StereoToolMac LogoWindows Logo & Melda's MStereoScopeMac LogoWindows Logo.

  • Stereo Array Calculators: If you want further help designing a stereo microphone array for a specific session, here are a few of the most useful resources: my personal favourite is Helmut Wittek's Stereo Image Assistant (although it requires the latest version of Java to run, and it's worthwhile reading Wittek & Theile's 'The Recording Angle -- Based On Localisation Curves' if you want to get the best out of it); Eberhard Sengiel's web-based stereo-array visualisation page; and Michael Williams's well-known 'Stereophonic Zoom' article from Rycote's Microphone Data site.

FURTHER READING

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