"High Fidelity in Recording" - EMI

High Fidelity in Recording

The pursuit of "High Fidelity" has spread rapidly in recent years. No longer is it regarded as a mysterious cult practised only by the technically initiated; an ever-growing number of music lovers and record enthusiasts are coming to realise that there is far more in a good record than they have yet got out of it, and in striving for ever higher standards of reproduction they are reaping the reward of greatly increased pleasure and enjoyment in their listening.
It may be as well to start by finding an acceptable definition of what "High Fidelity" really means — partly because it may not necessarily mean the same thing to everybody; partly because musical listening and appreciation must be largely subjective; partly because it will help to bring our objective into clearer focus.

High Fidelity - A Definition
Let us say, then, that High Fidelity implies the creation, in the listener's normal surroundings, of the ILLUSION of the actual performance as it would have been heard under the most favourable conditions.
This definition postulates several important considerations. There are bound to be wide variations in listeners' normal surroundings: in the size and shape of their rooms, the acoustic conditions and so on. The scale of the reproduction is also important, in the same sense as the perspective of a photograph. A picture taken with a tele-photo lens tends to look foreshortened when viewed at normal distances, but if it were viewed at a distance comparable with the scale of the photograph, the perspective would appear in its proper proportions.
The analogy is not, perhaps, quite exact, but it may serve to illustrate the point that there is an optimum level of reproduction if the scale and perspective of the original performance are to be preserved in their true proportions.
Again, consider the case of a listener in the auditorium of a concert hall sitting, let us say, at one end of the front row, only a few feet away from the bass section of the orchestra. His subjective impression of the tonal balance and perspective of the orchestral sound might be quite different from that of another listener at the opposite end of the same row, while neither would receive the same impression as a listener in the back row. The divergences would be even more marked in an acoustically bad hall.
Therefore we say that the purpose of High Fidelity is to create the ILLUSION of the actual performance as it would be heard under the most favourable conditions.
It will now be obvious that its attainment must encompass a sequence of operations in which these and many other variables must be taken into account at some stage from the recording of the performance to its reproduction by the listener in his home. Part of this task falls to the recording engineers, but at the reproducing end the responsibility falls entirely on the listener, his reproducing equipment and the way he uses it.
It is the paramount concern of the manufacturers of "His Master's Voice", Columbia and Parlophone records (Electric and Musical Industries Ltd.) to supply a product which, used in conjunction with suitable reproducing equipment, will bring into any home the complete illusion of the original performance, and it is hoped that the information in this booklet will materially help interested listeners to extract the full beauty of the reproduction of which these records are capable, to their greater satisfaction and enjoyment.

Recording
Music is a universal language, and gramophone recordings, like a written or printed score, must be truly international. A work recorded in one country must be capable of being played in any other country with a uniformity of faithfulness to the original performance. This happy result has been secured by general agreement on standards of records, speeds, groove shapes and frequency characteristics embodied in the latest British Standard Specification No. 1928/155, which has now been adopted as a world standard by international agreement. All E.M.I. records are now made to these standards, no matter where the recording originated.
This may have been in a recording studio, a concert hall, a cathedral, a theatre or opera house. or even in the open air. Such a wide variation in recording conditions means that there can be no hard and fast rules about the acoustics of recording; only the long experience and judgment of the recording engineers enable them to reconcile all the variables and produce a result which accurately conveys the authentic "atmosphere" or the original performance.

Recording Characteristics
The recording characteristic determines the response of the recording system with respect to frequency. In practice, it is almost impossible to define a comprehensive recording characteristic, because, to be of any value to the record user, it must take in the whole of the system, including microphones, microphone placing, and studio acoustics. For example, consider an ideal system in which all the components of the chain, including microphones, have a perfectly flat response. Imagine that two microphones are in use, placed say five feet apart in an acoustically dead, non-reverberant space, and that the direct sound is approaching in the line of the microphones. At a frequency of 220 c/s, with a wavelength of 5 feet, the microphone outputs will be in phase, and the output will be almost double that from a single microphone. At 110 c/s, for which 5 feet is a half-wavelength, the microphone outputs will he in anti-phase, and the combined output will be almost zero.
In a practical case, this result is very greatly modified by reflected sound from studio walls, etc., and, of course, by the direction of the initial sound wave, so that the true response of the system is different for every instrument in the orchestra. When recording the larger instrumental combinations, it is rarely possible to obtain a good simulation of natural sound on a single channel using one micro-phone, since a microphone with ideal directional properties has not yet been devised.


Fig. 1. An orchestral recording session in progress at E.M.I. Studios. No. 1 Studio,
where this photograph was taken, is the largest, and is specially designed for orchestral recordings.
Other types of Studios are used for recording smaller groups, instrumentalists, vocalists, etc.

This example illustrates one of several reasons why it is necessary to be very careful when quoting and assessing a recording characteristic.
At the E.M.I. Studios, it is the practice to equalise each item in the recording channel, including microphones, to as flat a response as practicable, in order to ensure a good theoretical starting-point. It is then the job of the recording engineer to adjust conditions in the studio, and to combine the outputs of the various microphones, in order to produce from the monitoring loudspeaker a sound which satisfies the musical director and the artist, as well as his own technical judgment and critical comparison with the original sound as heard in the studio. The relationship between the waves on the recorded disc and the signals fed to the monitoring loudspeaker is held within very close limits, and it is this relationship which defines the recording characteristic.
When the recording is replayed through a system having a frequency response which is the inverse of the recording characteristic as defined above, through the same loudspeaker in the same room, the sound is in fact virtually indistinguishable from the original sound as heard on the monitor. This inverse characteristic is recommended as the ideal replay characteristic, though it should be borne in mind that, from the record user's point of view, it may be modified to some extent by the type of loudspeaker in use, by the acoustics of the listening room, and by the personal taste of the listener. To cope with such modification, most reproducers are fitted with tone controls.
This interpretation of the term "Recording Characteristic" permits originals from any source to be re-recorded at the studios, and for the re-recording characteristic to be adjusted, so that the finished record will match the recommended replay characteristic, whatever its original characteristic may have been. The optimum characteristic is dependent on the size of the groove and stylus tip, so that different recording and replay characteristics are required to make the best of the two sizes of groove in common use.