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Idiot's guide to audio equipment for broadcasting
You certainly plan to broadcast some kind of audio material, don't you? Whatever your
needs might be, here are basically two typical setups that can help you get going (see below).
Whichever you choose, balanced audio inputs almost always make a big improvement. Balanced
audio inputs help eliminate noise generated by ground loops or strong RF fields. A hum experienced
with unbalanced audio wiring usually magically dissapears as soon as proper balanced cabling is used.
Check our SE4 DSP+ and microMax ST-1 stereo encoders, they feature balanced inputs.
PC-based setup
If you have a strong enough PC consider using it for managing audio part of your radio station. There are many specialized computer programs
available for this purpose. Winamp, which is not specialized for this purpose, does a pretty good
job (the pic is below) since it can play most sound formats, including MP3. Many plugins exist, making it possible to schedule music and perform all kinds of processing and functions.
Winamp supports various plug-ins. Plug-in is an add-on to a program that you can use to
add functionality. Audio-stocker is one of the better ones. It seems to be perfectly suited for broadcasting. It provides FM-station-like compression,
at no additional cost (provided you own a PC and a sound card).
A PC with sound card and suitable software CAN actually take care of most of your audio processing needs, at least in the beginning.
As your station grows you eventually need to purchase DSP stereo encoder and proper compressor and limiter.
Classic setup
Many professional DJ's that I know hate using computerized audio systems. They say
that PC's can let them down, we all know the good old blue screens that Winblows produces now and than and a crash in the middle of a hot show can take you offline for a couple minutes at best, a disaster.
Beginner would probably start by plugging his CD or cassette deck directly into his transmitters
audio input. However this is not a proper way of doing things. Classical setup would be something like this:
1. Preemphasis circuit
This is typically part of the stereo encoder itself, it raises level of higher frequencies in audio.
Higher frequencies are then attenuated in receiver. This technique lowers level of noise in received signal.
2. Low pass filters
Audio signal has to pass low pass filter before it goes into stereo encoder. Audio signal should not appear close to
19KHz as this is where stereo PILOT is and it would cause the Stereo LED on the receiver to flicker as well as receiver
shifting to MONO mode. Even if you transmit in MONO, such low pass filter should be used. Why? To limit space that your
signal uses on the band. Your signal could become wider than the standard deviation for FM broadcasting, resulting in
interference to other radio stations. Interference means you can get busted!
3. Audio limiter
Makes sure your signal never gets too far from center frequency. A maximum deviation of 75KHz should
never be exceeded since that means interference to adjacent channels.
4. Compressor
increases your average loudness while not exceeding maximum allowable deviation. Pushing this too far will make you sound distorted. The general trend
nowadays is to push compression above all reasonable limits.
5. Stereo encoder
choose wisely when you're shopping for stereo encoder and most of the above can be yours in a single device. Our SE4 DSP+ performs all of the above without
breaking a sweat. Give it a try!
6. Microphone, Mixer, CD players, DAT recorder, turntable...
A dat recorder is handy for recording commercials etc. A mixer is pretty much a must. Pushing real sliders beats will never be the same as clicking with a mouse.
A microphone, of course, CD players, usually at least two, perhaps a turntable (if you've got plenty of old vinyls)!
NOTE: Always keep your aerial away from your audio circuitry and audio cables, power supply and even transmitter.
If you cannot meet these requirements, you could experience feedback and other RF problems. Strong RF field
can make CD players and other digital devices go bezerk.
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