I have been asked several times why I have chosen an external microphone processor. So, I thought it was time to put my reasons down on paper.
Some new amateur radio transceivers come with a reasonably good microphone and sound quite good when set up correctly. However, I'm not a hand-mic type of guy, and I'm also not a desktop kind of guy. When using a desktop mic, I either end up needing to go to the physio more often to get the knots out of my neck or it ends up becoming a "hand-mic".
Throughout my pursuit for a well-balanced SSB transmit audio, I have learned a little bit about audio bandwidth and how to squeeze my dulcet tones into less than a 3.3kHz audio bandwidth.
But I digress. To answer the question, I went with a dynamic studio microphone, and for that, I needed outbound amplification to drive the microphone. I also wanted/needed a bit of equalizing and compression to the audio signal. Additionally, I wanted to restrict some of the background noise that we all seem to endure at odd occasions. Therefore, my requirements became the following:
- It needed amplification.
- I also wanted rudimentary filtering (EQ).
- It needed noise gating.
- It required compression that is smooth.
- It should fit my hobby purse.
With my wishlist sorted, I looked at what was available at a reasonable price. There are a lot of processors available, but most of them break my hobby purse. However, I finally found that the dbx286s ticked all my requirements, including requirement #5, the cost.
Here is a quick rundown of how the dbx286s fulfills my requirements:
1. Amplification: The pre-amplifier gain control runs from 0dB to 60dB, has 48V PHANTOM POWER if a condenser microphone is being used, and an 80Hz High Pass Filter (rumble filter) to take care of any rumbling at low frequencies. This is a very steep 18dB/octave high-pass filter. This filter will also, to some extent, reduce the proximity effect one gets with directional microphones.
2. Filtering: The dbx286s has a two-stage enhancer, the LF DETAIL and the HF DETAIL. Most enhancers work by adding a controlled amount of distortion to the audio signal. However, the dbx286s functions like an equalizer. One interesting aspect is that the LF DETAIL control applies a boost at 80Hz and a cut at 250Hz simultaneously. Many of us are aware that boosting low frequencies will often make the sound quite muddy. However, this "muddiness" is usually due to boosting frequencies other than those that would subjectively add bottom end to the signal.
3.Expander/Gate: Gating the audio signal to reduce background noise is a bit of an art form, and it took me quite a while to get it right. On the 286, there are two adjustments we can apply: THRESHOLD and RATIO. The ratio is adjustable up to a level of 10:1, and the threshold is variable from OFF to +15dBu. This allows me to reduce low-level clutter in the audio signal, such as breaths, without affecting the vocal itself. It's important to remember that compression raises the noise floor of the audio signal. The expander has two LEDs, one red (-) and one green (+), indicating when the audio signal is below or above the threshold. However, I found setting the gate was easier by listening to my transmitted signal on a second receiver.
4.Compressor: The compressor has two adjustments: DRIVE and DENSITY. The compression is of the over-easy type, which means the ratio increases as the audio level gets higher. This means that the Drive control controls the degree of compression. With just these two controls, I can get a very smooth compression and apply it carefully to avoid sounding over-compressed. Additionally, the 8-stage LED bar-graph shows the amount of gain reduction occurring during compression. This is quite different from the compression used in AR transceivers.
5.Cost: Yes, I achieved this requirement. The microphone and microphone processor, at the time of purchase, set me back slightly over $0.6K.
