SRA stands for Stereo Recording Angle and it helps to predict how well the stereo position will translate when reproduced over monitors at the standard 60 degrees apart. For example in a stereo array with an SRA of 90 degrees, sound sources at 45 degrees from the centre line will appear to come from the position of each speaker. Anything inside the SRA will be localised as a phantom source somewhere between the speakers and anything outside the SRA will be out of phase or even sound as if it is coming from the wrong side!
Timing And Level Differences
In a stereo recording using a stereo mic array the position of sounds in the stereo panorama is inferred by the listener by interpreting the level and timing differences captured by the mics. There are several variables which come into play here. The polar pattern, the mutual angle between mics in a coincident array, the timing differences between mics in a spaced array or both in a near-coincident array. Other variables are the width of the sound sources and the distance from the sound sources.
As we can see there are several variables at play and there is more than one "correct" array for any given situation. The interdependence of these variables always reminds me of the interdependence between aperture, shutter speed and ISO in photography: There is more than one solution which will capture an image correctly and an element of taste and preference comes into play between the various correct options - but there are definitely "wrong" solutions.
Unsurprisingly Neumann understands SRA and to make it quicker and easier to identify the "correct" options their free iOS and Android app allows quick experiments to find out exactly by how much you need to change the mutual angle between your mics if you change some cardioid mics for hypercardiods.
Watch the video to see it in action