The mixing desk metaphor found in Digital Audio Workstations (DAW) is built upon a specialised and technical knowledge of signal flow and audio engineering. However, since their inception the DAW has gained a far wider and less technically specialised user-base. Furthermore, the limited screen space of laptop and tablet computers, combined with potentially limitless tracks in current DAWs has resulted in the need for complex interface navigation during mixing which may inhibit a fluid and intuitive approach to mixing. The research outlined in this thesis explores novel designs for Graphical User Interfaces (GUIs) for mixing, which acknowledge the changing role of the user, the limited space of tablet and mobile computers screens and the limitations of human perception during cross modal activities (aural and visual). The author designs and conducts several experiments using non-expert participants drawn from several music technology courses, to assess and quantify the extent to which current DAW designs might influence mixing workflow, aiming our research especially at beginner and non-expert users. The results of our studies suggest that GUIs which load visual working memory, or force the user to mentally integrate visual information across the interface, can reduce the ability to hear subtle simultaneous changes to the audio. We use the analysis of these experiments to propose novel GUI designs that are better suited to human cross-modal perceptual limitations and which take into account the specific challenges and opportunities afforded by screen-based audio mixers. By so doing, we aim to support the user in achieving a more fluid and focused interaction while mixing, where the visual feedback supports and enhances the primary goal of attending to and modifying the audio content of the mix. In turn, it is hoped this will facilitate the artistic and creative approaches required by music computer users.