The evolution of microphones has been so influenced by broadcast applications over the last 80 years that one could almost say that every microphone is a broadcast microphone. Ever since the beginnings of widespread radio broadcasts in the 1920s, new technologies and changing requirements of broadcast have led to improvements of, or modifications to, existing microphones.
Microphones such as the Georg Neumann BCM 104 are increasingly incorporating as many features of external accessories as possible, and offer an almost plug-and-play approach that is well-suited to single-person studio operations.
The transducer principles were adapted to a wide range of broadcast requirements and specialized applications, including studio mics, miniature lapel mics, highly directional shotgun and parabolic mics, radio mics, and digital mics. For all of these applications, the main aim is to provide the best possible signal quality, adapted to the specific sound source, and to sometimes adverse recording surroundings.
Dynamic and condenser
While all basic transducer principles were already established by the 1920s, those that remain popular are moving coil dynamic and condenser. Dynamic microphones are most simple to use and require no power. Condenser microphones are inherently more fragile and generally more costly than dynamic ones, but they have proven to be the most detailed and precise transducers. Furthermore, they can be miniaturized, which is essential for picture-related applications.
Smaller and more directional
TV led to the development of unobtrusive small microphones in the 1950s. In this context, small means cylindrical microphones with roughly a 20mm diameter. This type of microphone is still used for most ‘neutral’ recordings, be they of musical, vocal or ambient signals.
The TV and film industries also necessitated the development of highly-directional microphones. Shotgun microphones were developed in the 1960s for film and TV sets with a prevailing high-ambient or audience noise. Here, directionality and the attenuation of ambient noise are the relevant factors, although some off-axis sound coloring must be tolerated.
Parabolic microphones, i.e. standard small microphones mounted into a large parabolic shell, are even more directional. But their overall sonic behavior limits their use to applications such as sports broadcasts where, for example, the sound of the ball on the soccer field must be followed.
Solution D, Georg Neumann’s D-01 digital microphone, features an integrated A/D converter, 130dB-A dynamic range and de-esser.
Further miniaturization became possible with electret microphones, i.e. very small pre-polarized condenser microphones with limited power requirements. When combined with RF transmission of the signal from a body pack to a distant receiver, these form the backbone of most TV shows and interviews. As lapel microphones, or even hidden in the artist’s hair, they can be placed very close to the sound source, thus offering a high direct signal component, although their comparatively high noise precludes their use in other applications.
The omnidirectional microphone is comparatively insensitive to all wind and pop disturbances. Therefore, it often can be used without any additional protection for applications such as interviews. Directional microphones, on the other hand, do accentuate any outside disturbances and, therefore, require internal or external protection against wind and pop.
While a vast range of accessories is available for all different situations — from foam wind shields, nylon gauze pop shields and solid windshield cages to the additional fur overcoat used in extreme wind situations — the often hectic environment of broadcast demands ease of use. As a result, specialized microphones should integrate protective measures against the type of disturbance they are likely to encounter in their typical working environment.
Microphones are increasingly incorporating as many features of external accessories as possible, and they offer an almost plug-and-play approach that is also well-suited to single-person studio operations.
Electret microphones are being further miniaturized, with detail on safety and protection issues such as humidity, sweat, soiling, and wind and pop disturbances. These microphones also are used in headsets that combine microphone and headphones. Although they seem easy to use, they generally demand a trained speaker, due to the microphone being positioned very close to the mouth.
Shotgun microphones are already a highly-developed species, whose directionality cannot be much improved on. Multi-microphone array techniques, as used in loudspeaker line arrays, are mostly still at the research stage and rarely provide sufficient quality for broadcast. Over the last 10 years, stereo shotgun implementations have been introduced, combining spot and ambience microphone capabilities in a practical combination.
For surround sound, one can only speculate on future ‘standard’ microphone setups. Audio engineers have been experimenting for years with different multi-microphone geometries, but it seems to be getting clearer that only new techniques on setting the microphones up are needed, with perhaps some additional accessories, but not any new microphone technology.
The microphone itself is finally becoming digital. The AES has implemented the AES 42 standard on ‘Digital Interfaces for Microphones,’ thus providing the backbone for current and future products, along with their powering and synchronization requirements. Digital microphones integrate a host of additional aspects — analog-to-digital (A/D) conversion, amplification and digital signal processing such as de-essing. This greatly simplifies the microphone signal chain. With internal A/D converters with a very wide dynamic range up to 130dB-A, for example, gain-setting issues may become a thing of the past. Future implementations may even make further external components, such as limiters and noise gates, obsolete.
Today’s microphones are already well-developed performers. As far as signal quality is concerned, there is hardly any room for improvement. Digital broadcast technology, however, will increase the demand for digital microphone solutions, and such further specialized and adapted microphones will make the sound engineer’s job simpler, while stereo and surround applications will present additional challenges.
Martin Schneider is the microphone development engineer for Georg Neumann.
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