A powered mixer is an all in one amplifier and mixer. Combining the two means there is less to carry when travelling, the overall setup is less complicated and the components are perfectly matched. Sound can be played with the mixer directly connected to speakers. In cases where the same equipment is always connected, powered mixers can be used by simply turning the power on, so operation is simplified and convenient.
The number of input channels in a mixer is extremely important, as this indicates the number of microphone and musical instrument signals that can be handled. In addition to the number of input channels in a mixer, it is also important to consider such factors as how many of those input channels are for microphones, whether line input channels are monaural only, and whether inputs will accept stereo signals.
Mixers can output various separate channels of audio, depending on the needs of the event, such as sending audio meant for the audience to the main speakers and audio meant for the performers to the monitor speakers on stage
The aux bus is a circuit used to send signals to external devices. It can be used to send signals to performers' monitor speakers separately from the main output, or to send signals to external effects and recording devices.
The group bus is a circuit for controlling multiple channels at once. For example, if there are eight microphones (for eight channels) placed around a drum set and you want to raise or lower the volume of the entire set, it would be difficult to accurately raise or lower the faders for all eight channels. If these channels are all set to a single group, the volume of the entire drum set can be raised or lowered, while maintaining the same balance, merely by raising or lowering the fader for the group.
The stereo bus is a circuit for combining each input coming into the mixer or each group bus signal, adjusting the overall level, and outputting the audio through stereo output connectors.