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9 - THE INTERPRETATION OF MICROPHONE DATA SHEETS

Sensitivity - Max SPL - Noise Floor - Dynamic Range

The analysis of microphone specifications is an important part in the process of choosing a microphone for a specific sound recording situation. Before the publication of the Rycote Microphone Data on CD-ROM (and now as a web-site), the assembling of all the data concerning different microphone specifications was no mean task. In fact in some cases it was doubtful even if manufacturers really wanted their customers to read and to understand these specifications! All credit to Rycote and Chris Woolf, the editor, for their effort in the presentation of the microphone data. The publication of this data in a formalised and neutral format is a major advance in helping the sound recording engineer to make a reasoned choice of a microphone for a particular usage. In most cases this information must be used in conjunction with the more subjective appreciation of sound quality transmitted by the microphone under operational conditions. However nothing can replace the initial selection based on a comprehensive analysis of the basic specification of the microphone.

In respecting the now international standards for the specification of the different characteristics of a microphone Rycote have at last brought a certain degree of uniformity to all the available information. However the uninitiated should still be forgiven for thinking that these characteristics remain rather difficult to integrate into the practical world of sound recording. There are very good reasons for the form in which each of these characteristics is specified. But an overall view of these characteristics, enabling one to make an intelligent comparison between microphones, still remains rather difficult.

However you should not be surprised to hear that any improvement in understanding the signification of these specifications also needs some additional effort by the reader. The effort to be made is, wait for it --- is in the use of “logarithms” and “decibels”. But we are thankfully far from the days of logarithm tables and slide rules. So nobody should refuse the simplicity of hitting a few buttons on a calculator to get this microphone data jargon into more understandable form. And please don’t blame Rycote for not transforming the microphone data, remember they have used the international standard format for each characteristic within the specification of a given microphone, as supplied by the manufacturers. For the time being, it is therefore up to the user to transform this information, according to his needs.

We need to know the general sensitivity of the microphone and how this will relate to the input stage of, for instance, the mixing desk. We also need to know the total dynamic range within which we can position the dynamic of the sound source. This second characteristic obviously implies knowledge of both the maximum sound level that can be accepted by the microphone and transmitted to the next stages of amplification, and of course the noise floor of the microphone. With the advent of digital technology we now have available a remarkable dynamic range within which we can record. This does not however exempt us from the need for careful matching of the dynamic range of the sound source transmitted through the microphone, to the mixing desk, to the various processing equipment and eventually to the recording media.

Headroom must still be allowed for, in order to accommodate unexpected high level signals, and the very low signal levels must obviously be well above the general noise floor, be it acoustic noise in the studio, electric noise generated by the microphone or the mixing and processing equipment, or simply the noise floor of the recording medium. In some cases the noise floor can even be determined by a specific listening environment such as the automobile!