Armed with the theory of mixing, music producers can approach the mix on a more practical level. The first stage consists of cleaning up the audio tracks with a noise gate and removing unwanted frequencies from each instrument track with some aggressive Equaliser. While all the harmonics are required to reproduce a sound in isolation, in the context of a mix many of the upper and lower frequencies can be removed with a shelving filter. A conventional and useful technique for mixing is to monitor the output of the mix in mono. Proponents argue that mixing through a compressor helps readers achieve the sound of dance music because it glues the mix together, and is a preferable alternative to placing the compressor on afterward as it can upset the mix. By using an analog device to sum channels together in the digital audio workstations, it produces a more robust soundstage with air and presence.