Here are some hints to having great audio within 3kHz of bandwidth on amateur radio. I actually run 2.8kHz. 100-2900Hz, with fantastic results.
As Bob Heil says, it all begins at the microphone. And he is correct. Use a high quality mic, no matter the brand you choose. Use high quality mic cable and connectors. If you construct your own cable (I do) pay close attention to all solder connections.
Station grounding. This is extremely important to transmitting clean audio. Unfortunately many hams skimp on proper (rf) grounding. Don’t be that person.
Understand the settings in your radio. Unfortunately many hams have no clue on how to properly setup their rig, due to having never thoroughly read, and understand the operators manual. Truth be known, their operators manual is probably stored away in the shipping box the transceiver arrived in. These people stick out like a sore thumb on the air. Don’t be one of them.
Listen to your audio with some high quality headphones using the monitor feature of your transceiver. By doing so, this gets you in the ball park of the correct settings.
Once you sound decent with the monitor feature of your radio, use a 2nd high quality receiver to listen to your actual transmitted audio. Don’t have a second receiver on hand? Use a on-line SDR to listen to yourself. Make any necessary adjustments to your transceiver as needed.
Once you have your settings to your likings, get on the air and make some contact. Always monitor your ALC. I found an average of 75% ALC works best for me. Avoid compression/processing as much as possible. There is a time and place for compression/processing. This is not that time.
As you are making contacts, NEVER ASK anyone how you sound. If you sound good you will receive UNSOLICITED comments. Once you begin receiving these UNSOLICITED comments, leave your settings alone. Don’t be one of these LIDS that re-adjust their setting each time they get on air.
A word about outboard audio gear. Is it necessary with the current transceivers on the market? For most, the answer is no. Especially if you’re using a modern Yaesu or Kenwood. Several of the newer models have a parametric eq feature. Learn it! As for ICOMS’s I can’t say with certainly they have this feature. From what I’ve been told most ICOM’s only have a bass and treble setting. It’s possible that many ICOM’s would benefit from outboard audio gear due to the lack a parametric eq function.
In closing. The above is simply a primer for transmitting good, articulate audio. Complete guide? Absolutely not. Depending on your situation you may have to go an extra mile to achieve your goal. However, once you reach that goal, STOP screwing around with the settings! Remember you can not please everyone, and everyone’s receiver may be setup differently.