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5 Stereo Recording Microphone Techniques

  • alex22watts
  • May 8
  • 6 min read

by Alex Watts


5 Microphone Techniques to achieve the perfect stereo image


Recording in stereo can help to achieve depth and a sense of space to your audio recordings and can be used to reproduce an accurate and detailed stereo image of an ensemble or a less true-to-life representation of a specific instrument for some ear candy. Here are my 5 favourite ways to do this and the benefits of each technique:


At university, I decided to focus part of my dissertation on Stereo Recording Techniques, testing and analysing several different techniques as I recorded my own compositions. Since achieving a first class result with this project, these techniques have continued to serve me well as a live sound engineer and in the studio as I utilise these techniques on almost every gig or recording session. Having an arsenal of techniques to choose from can help to achieve the exact result that you want, rather than just opting for the same single mic placement each time, so here I aim to introduce you to a handful of options for you to try.


Here are 5 stereo microphone techniques for you to try out on your next session.


Techniques

Near-Coincident Pair (ORTF)

Mid-Side

Spaced Pair


The Spaced Pair Technique is the most simple to implement and is a solid option for a number of applications where other techniques listed below may not be as practical.

This technique utilises two microphones, preferably a matched pair of the same make and model, placed apart at different positions in front of the source. To determine the spacing, use of the 3:1 rule will help provide a minimum distance: the second microphone must be at least 3 times the distance from the first microphone as the first microphone is to the source.

Using this technique gives you some flexibility with mic placement, unlike with many of these techniques where the microphones need to be close together. The benefits of this are that you can capture a wide stereo image of a large instrument or ensemble or use this technique for your stereo room mics or to capture orchestras.

This technique can also be used to close mic specific instruments such as guitars or pianos, as the flexibility to position the mics sepaprately around the instrument can allow you to refine the positions in order to get the sound you need, rather than compromise by moving both together. With guitars, for example, you might choose to mic the 12th fret and soundboard of the guitar, or try 12th fret with an over-the-shoulder position, giving a different character to the recording, changing the feel and stereo image. For pianos, it might allow you to position one microphone over the bass strings and one of the mics over the treble strings.

The stereo effect is created due to the difference in arrival times and level of the sound source between the two microphones; due to the microphones being placed apart, this can differ greatly, delivering separation and a wide stereo image. The caveat to this technique is the fact that the phase difference can sometimes be quite pronounced and is therefore more susceptible to audible comb-filtering and is less mono compatible. However, this technique is very useful and I use it often for drum overheads, guitars and room mics.


Try this on your next recording session!


Coincident Pair (XY)


Considering the previous technique's potentially negative downside of audible comb-filtering; the coincident pair is a technique that aims to minimise this entirely, resulting in a cleaner and more defined stereo image. I most often use this techniques with matched small diaphragm cardioid condenser microphones (see the cover image above). To position mics in a 'coincident pair', place the capsules of the microphones as close together as possible, perpendicular to each other, each at 45° to the centre of the sound source or ensemble.

Due to the microphone capsules being so close together, the source's soundwaves' arrival times to each microphone are near enough the same, minimising phase differences in the audible frequency range, whereas the sound pressure level at the two diaphragm will differ when a source is off centre to the mic array. The stereo field might not feel quite as wide as you can achieve with a spaced pair, but it is more accurate within the mic array's 'Stereo Recording Angle' (SRA) of 76°.

I use this when recording acoustic instruments, often as a stereo room mic set-up when an accurate image is required, and it's also another good option for drum overheads, as you can minimise phase issues caused by the differing arrival times of the snare and cymbals.


Blumlein

The original version of the previously mentioned coincident pair is the Blumlein technique, devised by Alan Blumlein in 1931 at Abbey Road Studios. This technique utilises a pair of figure-of-8 microphones rather than two cardioid mics, meaning that the off-axis rejection to the sides of each figure-of-8 pattern create better separation between the left and right microphones and a resultant wider stereo image. The figure-of-8 mics will pick up sound from the rear, too, making this a good choice for mic'ing a room, though the reverberant sound recorded at the rear of the mics will appear on the opposite side of the stereo field. This is said to be more realistic than a standard coincident pair arrangement. with a wider stereo image. It's one of my favourite techniques to set-up too and it looks really cool!

Near-Coincident Pair (ORTF)

A closely related technique to Coincident Pair is the Near-Coincident Pair technique. This adapts the placement slightly so that the microphone capsules are spaced apart by a few inches or so at an angle of 110° to the source but the microphones are still pointing in the same direction as in coincident pair (though facing apart now). The slightly spaced-out placement delivers a wider stereo image and more accurate localisation of instruments if recording an ensemble or orchestra; this is due to the fact that there is a difference in time-arrival of the sound to each microphone capsule and a difference in sound pressure level received at each capsule due to the difference in distance from the source.

The Near-Coincident Pair has a number of iterations. One of which, ORTF (Office de Radiodiffusion Television Francaise) utilises a spacing more akin to the distance between the human ears, which again improves the realism of the stereo field from the standard Coincident Pair technique mentioned above.


This is not a technique I have used all that often, as I more regularly opt for the spaced or coincident pair techniques, but the added realism and accuracy for source localisation make it worth utilising when recording ensembles, orchestras and choirs; which means I'll be sure to use this in future! If an accurate stereo image is what you're after, try this one out!


Mid-Side Technique

Mid-side utilises microphones of different polar patterns, one cardioid microphone on-axis to the source and one figure-of-8 microphone perpendicular to the caridoid microphone, facing side-ways (the front face to the left). There is some minor trickery to perform in order to set this up in a DAW or console; this involves panning the side mic fully left. then duplicating the 'sides' microphone channel, inverting the phase of the recording and panning it hard right - the two side channels can then be routed to a bus so that their level can be controlled simultaneously. The alternative is to use a mid-side encoder/decoder plug-in to do this for you!

Mid-side allows independent level control of the sides and centre positions, which therefore allows you to play with the perception of width of the stereo image. And because the 'sides' of the stereo image come from one single microphone and position, they are phase coherent and sum perfectly into mono!


Universal Audio Sphere DLX microphone

A bonus sixth technique for my list is the use of the Universal Audio Sphere DLX microphone, which I have in my arsenal of microphones. This is a modelling microphone which has two capsules, (front and rear-facing), which are perfectly phase coherent. Associated plug-ins allow you to choose between many different microphone profiles (including vintage mics) that the Sphere DLX can model the characteristics of, as well as their polar patterns and filters etc.


Using UA's 'Sphere 180° plug-in' in conjunction with the DLX allows you to benefit from the mic's dual-diaphragm composition to record in stereo. By turning the microphone through 90° so that the front faces left and the rear faces right, you can achieve a stereo recording using just this one microphone! Altering the polar pattern slightly can also allow you to widen the image, too. Or you can use this microphone in conjunction with the Mid-Side Technique described above!


I hope that these techniques give you something new and useful to try out next time you are recording, but even if they are familiar to you, it's great to be reminded of some options and inspire further research. There are some great sources for further reading, where you can explore these techniques in more detail, or discover some more advanced options, too!


Further Reading:



 
 
 

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