Sound and Fury

by Adam M. Farson VA7OJ/AB4OJ

Some radio amateurs have observed that the IC-756Pro series did not "sound quite right" to their ear - "too mechanical, clinical or artificial" for their liking. I would like to comment on this.

Having spent nearly 40 years in the telecom industry, I tend to look for the same things in an HF amateur transceiver as I do in a commercial or military telecom system - the ability to "get the message through" accurately, under a wide range of transmission-medium conditions. If this parameter is met - if I can understand what the distant operator is saying - then my requirements are fulfilled. If the received audio quality is slightly degraded in the process, due to severe filtering and/or noise reduction, this is an acceptable price to pay for optimum articulation and virtually perfect copy.

In a telecommunications system, I rank audio quality lower than communications efficacy. Of course I like to transmit a signal of which I can be proud - and invariably, the IC-756Pro III with the Heil GM-5/HC-5 earns me good audio reports. I also like a received signal which is pleasant to listen to, and does not cause listener fatigue; the IC-756Pro III has very good receive audio to my ear - especially when driving a good telecom-optimised headset.

However, if I have to bring the radio's DSP tools to bear to "pull up" an otherwise unintelligible signal, and the end result (whilst perfectly intelligible) is a little "rough" - well, I am ahead of the game because we "got the message through". Here is an example: During a recent sked on 15m with my friend Matt KK5DR, a band-limited noise spectrum about 2 kHz wide popped up on our frequency. By engaging the DSP Manual Notch and turning the control, I was able to pull Matt's signal right out of that stuff with optimal articulation and 100% copy. I defy any analogue radio to emulate this.

In the Icom IF-DSP-based radios, the DSP is the radio.

Ultimately, the radio purchaser will have to make his own decision according to what he prefers and values most. From my perspective, the signal-management power which DSP technology places in my hands has settled the debate in favour of a 100% DSP-based radio architecture.

Copyright  2007 A. Farson VA7OJ/AB4OJ. All rights reserved. Last updated: 05/26/07