As technology advances brings the adult webcam industry up to date camming with sound is expected but not necessary. It will heavily affect your earnings though if you are on a cam site that 99% of other users have sound. One exception that comes to mind is the “Chat Only” section on Adultwork.com (Click “Online Now – Directcam” then look for “Chat only – DirectIM”), they refer to it as DirectIM (Direct Instant Messenger), not to be confused with SMS chat as you still use the JustCamIt software to talk on a pay per minute basis but no video is sent. Adultwork.com is probably one of the very last sites to have this feature. It is recommended to have audio enabled (remember not to play copyrighted music in the background) at all times in order to stay on par with the vast majority of other cammers.
Nearly all webcams come with a prebuilt in microphone and for the most part these are perfectly fine to get you started, as time goes by and you are making a good portion of your income from webcamming you may wish to invest in a dedicated microphone. Up to £100/$130USD would be the recommended ceiling price for a dedicated mic. Headset mics are usually best avoided unless you are going for the gamer camgirl look. At the basic level the built in microphone is fine, next level for a basic dedicated microphone would be the Blue Snowball mic and heading toward a good mid range one would be the Blue Yeti, its very popular among camgirls.
Just like settings for your video feed your microphone will also have its own settings, this may be from the microphones own software or via streaming software the website you can on provides. If both instances are present you need to make sure the quality is setup correctly on both, no point having the microphones own software set to high quality when the streaming software is set to low. There is a good chance you have a plug and play microphone either built in or dedicated and you wont have have software from the products manufacturer which is ok.
Comparing two different streaming softwares:
This is a screenshot from OBS Open Broadcast Software, its an advanced streaming suite used by some big box sites by default.
And now JustCamIt (flash based streaming software).
A major difference in the two software is one supports mono and stereo and the other Justcamit only supports mono, nearly unheard of in modern times. Justcamit (flash based) was created back in early 2004 and has relatively few updates since, on version 3.0.8 currently while OBS (C++ based) was released in 2012 and has frequent updates keeping up with modern technology. Sites that use the outdated Justcamit software like Babestation.com and Adultwork.com will be upgrading their software in due time.