Living by numbers – The benefits of digital.
Having spelt out the advantages of using an analogue transport for wireless mics in a previous blog I thought it was about time I covered the up-sides of using an all digital system.
Firstly, let’s look at the basic difference between the two systems; whilst analogue FM uses a single carrier frequency the frequency of which is modulated by the audio feed, digital uses multiple carriers which take up the occupied bandwidth of the channel, usually 200kHz. As digital systems are sending a constant stream of data they always use the full bandwidth, even with no audio applied.
One of the things you can do with digital wireless systems that is impractical for analogue is to encrypt the audio so that it cannot be intercepted by unauthorised persons. This can be very useful for corporate applications or high-profile productions where one would not want any of the dialogue to be leaked by unscrupulous, scanner wielding reporters!
Then we come to audio, this can be flatter and more phase coherent than analogue in a well designed system. One has to remember that, in order to squeeze 20kHz audio into a 200kHz wireless channel one needs to use some form of compression, simply sending uncompressed CD quality would require around seven times the bandwidth available. Different manufacturers approach this in different ways, but, in general the audio passed through a digital system is more predictable than an analogue system with companders which can produce unwanted artefacts.
If you suffer from co-channel noise, digital simply mutes the audio when the difference between the radiomic signal and the underlying noise drops below the threshold (the carrier to noise threshold of wireless systems varies between different manufacturers and modulation schemes). On the other hand, analogue systems will suffer from background whistles and other unwanted noises in a similar situation.
In summary then, all-digital wireless mics do offer clear advantages over analogue systems, and in a controlled environment can provide very high-quality audio, reliably and securely.
As is so often the case it’s horses for courses, and the best choice for a given situation will depend on the actual requirements. Digital really shines when you have a clearly defined field of play.
Written by Pyers Easton, MD of Raycom Ltd Evesham.