How's My Audio?
by Tom M.Morton
Written for the PARC newsletter, Newport News, VA
"Your audio really sounds great, so glad you asked!!"
Since we can't get our fingers in the magic boxes we use for radios these days, many of us have turned to playing with our transmit audio. It seems to be a growing trend. We all want those unsolicited compliments about how great our audio sounds. If you have spent much time on the HF bands recently, you have heard everything from beautiful to strange and un-copyable. The FCC gives us a 3 Kc bandwidth for SSB communications, and many radios won't pass more than 2.6 or 2.8 Kc. Also, most radios won't receive with a bandwidth any wider. This is more than enough for passing the essence of the human voice, and making it sound excellent.
Many have doctored their radios to transmit with a wider and lower frequency passband, and have done it unnecessarily and possibly illegally. Some transmit audio that goes from 50 cps to as high as 4 or 5 Kc. They produce a signal that is difficult to tune and copy for most. They have employed expensive microphones and racks of professional recording equipment. 90% of the capability, audio spectrum, and money are not used and are wasted, since we are supposed to use only a 3 Kc piece of it's 20 Kc capability.
I think a Ham should want audio that is smooth, clear, easy to tune, copyable with a weak signal, "broadcast quality", and that gets those unsolicited compliments. This is possible with out the expensive runaround, or the use of more than the legal bandwidth. The goal is a reasonability flat response from about 150 cps to 2.8 or 3 Kc. Any frequencies below 100 cps make the signal hard to tune and copy when the signal is weak. Since the low frequencies use more of the power in a SSB transmission, and don't contribute to the intelligibility, you want to use just enough to give it the "broadcast" quality. The difference in the sound of a signal with a 150 cps bottom and one with 300 cps is amazing.
What is needed is a good quality full range mic. These can be found easily for less than $100 and in many cases less than half as much. Most of the mics that are sold by radio manufacturers don't have the low frequency response needed. If your radio has some internal equalization, you will want to adjust it for the best sound. If not, the best bang for the buck is the W2IHY equalizer. Speech processors should not be used and care should be made not to exceed the ALC level for your radio. The best is to not pull any ALC at all. Then find someone on the air that has audio that you admire and he will be all too happy to help you with the adjustments.
Some of the best audio I have heard was made with just a moderately priced mic and the radio alone. On the converse, some of the worst was made with expensive mics and racks of equipment. The more stuff you have in the audio chain, the more adjustments you have to make correctly. Its much easier to saw the legs off of a four leg table than a ten legged one, so keep it simple. With just a little effort and money, you won't have to ask, "How's my audio", they'll tell you it's beautiful.