![]() Wollschaf ( CC BY-SA 3.0).įor the purposes of FM broadcasting, the left and right channels are combined into sum, or L+R that represents the mono component, and a difference between the channels, or L-R. ![]() Aboce the audio on the left is a 19kHz pilot tone, then the stereo difference signal modulated on a 38kHz carrier. The Last Bastion Of Analogue Stereo All the information in an FM stereo broadcast, represented as a spectrum. This features a system in which the main broadcast is in mono, but the stereo information is separately encoded on the transmission at an inaudible frequency for decoding in the receiver. There is however one place in which you’ll still commonly encounter a stereo source that uses an analogue encoding system, namely FM radio. Meanwhile in digital audio systems the left and right channels arrive as bitstreams either from an interleaved i2S source such as a CD player, or from a decompression algorithm in for example an MP3 player or internet streaming software. In an analogue tape deck or a vinyl record the stereo channels are recorded separately as tape tracks or opposite sides of the groove. Thus a stereo recording created from a mix of mono recordings can best be referred to as pseudo-stereo because it lacks that phase information which gives the stereo recording so much depth. In the modern era, a true stereo recording picks up much more than the relative intensities of different sounds, it records the complex web of timing and phase differences in the sound including those in the background noise. Listen to “Yellow Submarine” fully panned. For example, a band could have the bass guitar placed mostly in the left channel and the lead guitar in the right, with the drummer and vocalist equally in both channels to place them in the centre. On the face of it, a stereo recording delivers only left-right positional information, and thus can be created from a series of mono tracks by adjusting their position in the stereo mix. His work laid down the fundamentals of stereo recording, including microphone configurations and what would become the standard for stereo audio recording on disk with the channels on the opposite sides of a 45 degree groove. We have one of his stereo demonstration films in “ Trains at Hayes“, filmed from the EMI laboratories overlooking the Great Western Railway, and featuring a series of steam-hauled trains crossing the field of view with a corresponding stereo sound field. Stereo recording as we know it was first perfected as one of the many inventions credited to Alan Blumlein, then working for EMI in London. Instruments appear to come from their relative positions when recorded, and the sense of being in the performance is enhanced. These are then played back through a pair of speakers, and the result is a sense of spatial field for the listener. It’s a word so tied-in with Hi-Fi that “a stereo” is an alternative word for almost any music system, but what does it really mean? What makes a stereo recording, and how does it arrive at your ears? From West London Trains, To 3D Audio The driver of this Great Western Railway train had no idea that he was making audio history.Īs most of you will know, a mono recording uses a single microphone and a single channel while a stereo one uses two microphones recording simultaneously a left and right channel. In our last outing when we looked at cabling we left you with a promise of covering instrumentation, but now it’s time instead for a short digression into another topic: stereo. In our occasional series charting audio and Hi-Fi technology we have passed at a technical level the main components of a home audio set-up.
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