Heil on Sound

by Bob Heil, K9EID

(This article ran in Worldradio, June 2001)

Equalize that microphone!

Back in the AM days, it seemed as if everyone was conscious of their transmitted audio quality. Many of those signals had better response than the local broadcast stations. Good solid lows, crisp highs and very articulate midrange - just good clean balanced audio. Then came SSB and for years sounded very restricted as the transmitter bandwidths were set around 2.1 kHz - hardly enough for any high quality audio, either on transmit or receive.

The last few years has seen a movement on the SSB portions of the Amateur Radio bands to bring back higher quality SSB audio. Through major design efforts of the major manufacturers of transceivers as well as designers of microphones and outboard audio equipment we are able to put much higher quality signals on the air with little effort and low cost - in some cases, NO cost.

Choose the right equipment

Just as with anything else, you must choose the right equipment to do the job you are wanting to perform. Several of the major transceivers are now capable, through their DSP sections, to set the bandwidths at 100 Hz on the low end and 3,000 Hz on the top end. Still within the parameters of the regulations but absolutely what is needed to produce beautiful AM quality audio. It is extremely important to choose the right microphone that has a bandwidth from around 50 Hz on the low end through at least 12 kHz on the top end. The reason you will want a wider response microphone than your filters is so the rolloff of the filters is at least an octave from the roll-off of the microphone outer limit hinges. Anything narrower will not sound as smooth.

Equalization

Another important factor in selecting the equipment is to choose a transceiver with great variable DSP as well as variable transmit equalization and several of the latest generations of transceivers have built-in microphone EQ sections. If you don't have on board EQ there still is hope through the W2IHY 2-band or 8-band equalizer. With active equalization, you are able to adjust the amount of high and low frequency response, depending on the voice, the microphone element as well as the room ambiance. Active EQ allows you to balance the audio response exactly to the sound you are wanting to put on the air.

Recording studios and broadcast studios as well as every telephone, PA system and car radio uses some form of equalization to flatten the response curve and equalize it so you hear the voice in a natural balanced response. Bell Labs studied the human hearing responses for years and discovered the incredible lack of midrange sound the ear hears. The balance of highs and lows vary drastically with level and this is important to understand when trying to achieve clear, articulate, well balanced audio. As Bell concludes, our hearing is very sensitive in the mid-range and needs some help in the upper regions, while being very deficient in the lower extremes. Trying to copy the weak signals that do not have much midrange or high responses is much more difficult than copying those that are weighted in the mids and high regions.

Proper microphone techniques

It is so important to use proper microphone techniques so as to avoid extraneous background noises such as blower fans, TV sets in the next room, etc. Haven't you tuned across this big loud signal where the fan is louder than the stations voice? His explanation for the situation is usually that he is "running a lot of power" is certainly not the correct explanation of the situation. The problem is that he is usually speaking about a foot from the microphone with the un-equalized processor and mic gain cranked up - causing the background noise to be louder than his voice.

Microphones for communications transmitters were designed and meant to be within two to three inches of the user's mouth - no further away. It is NOT proper to sit back away from a microphone and expect to have that commanding signal. The important mid-range frequencies are lost, the highs are diminished and there is very little dynamic range. What is left is the room resonance that overrides just about any audio present.

To correct this and insure that your signal has that terrific mid-range punch, free from extraneous background noise, run the microphone gain as low as possible to achieve full ALC action and speak no more that two to three inches from your microphone. It is the accepted practice in professional communications and is the only way to achieve good solid transmit audio.

One of the major culprits that allow the operator to stay away form the microphone are the usual 'desk stands'. The best fix for this is to use a microphone boom as used in commercial broadcast stations as well as recording studios. The boom allows you to place the microphone two to three inches from your mouth and at the same time give you back the desktop that was taken up by that silly little desk stand! Using a footswitch to control the push to talk line of your transmitter in conjunction with the microphone and boom set up gives your station that terrific hands free operation and with great articulation into the microphone.

Paying attention to and practicing the simple science of audio at your Amateur Radio station will give you results you had thought not possible without spending lots of money when in fact great improvements can be achieved by simply applying the science.

Listen to your signal

Most of the transceivers have a 'monitor' section in their feature list but it is simply not the complete answer to exactly how you sound to the outside world. The only way that you know how you sound is to transmit into a dummy load and listen to a nearby receiver through a pair of quality headphones. Be certain that the receiver you listen to your transmitted signal on is listening in the same bandwidth of the transmitter. Remove the antenna, reduce the RF gain and set the receiver to a comfortable listening level as you step through the various bandwidth controls, mic gain settings and the all important equalization adjustments.

This is the only way you will really know how you sound to the outside world.

Have fun and keep all of those signals IN PHASE!

- Bob Heil, K9EID, our frequency response lovin' columnist can be reached by sending snail mail to: 5800 N. Illinois, Fairview Heights, IL., 62208-3505, or by e-mail to: bob@heilsound.com.

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