When planning a DJ or production live stream, audio is hugely important. For the audio to be usable in the event's archive you want the highest quality audio signal coming into your encoder. You could also use a separate audio recorder (as we've sometimes done) to record raw audio separately to your audiovisual broadcast.
USB or Firewire Audio Interfaces
The simplest way to capture high quality audio is through an audio interface. An audio capture card takes single or multiple inputs and gives you a basic level of control over the input's gain. There are too many interfaces to list so we recommend searching around. The interface often works via USB but Firewire and Thunderbolt capture cards are also available.
A mixing desk can do the same job as an audio interface (or be used in addition to a audio interface) but gives you more input and output channels. The benefit of this would be when taking in multiple audio feeds and being able to balance the volume of each in the output to the stream. You might have, for example, audio from the DJ mixer, a vocal mic and some crowd microphones. It's very important to be able to control each independently. Make sure you get a desk with enough inputs (of the right type) for your event!
If you have a separate audio recorder you may also benefit from a desk with extra outputs as well.
When capturing audio in an interview situation, Lavalier microphones are ideal. They clip onto the interview subject's clothes and offer clear vocal sound. They can be inexpensive and they're best used with a mixing desk.
When you're dealing with a crowd - large or small - adding in a little audio from the event transfers the live atmosphere to those watching online. For crowd mics, look for small condenser microphones. These are highly sensitive and capture audio from a wide area so are perfect at capturing the background noise of the crowd, as well as cheering and audience participation.
Condenser microphones require phantom power over XLR so make sure your mixing desk supports this.