Recently, one of my players suggested that streets and buildings felt too empty when we are playing Shadowrun. Other than many RPG, a lot of Shadowrun takes place in crowded cities, with the protagonists using the metro, casing a firm's lobby, or meeting someone in a club. So, usually there are lots of people around the runners and there is no shortage of things to see and hear around them, not mentioning information streaming in from their Augmented Reality overlays.
Even before, I usually made note of what kind of district they are in, and how that changes the type of buildings, as well as the types of people and activities they can see. I've described how Sararimen rush to work, how they have to weave through a crowd and someone bumps into them, or have had someone try bum a smoke from them.
Subsequently, I've been experimenting with ambience pieces from Tabletop Audio such as e.g. Dome City Center.
Obviously, it is beyond the capabilities of a GM to describe such an overcharged environment in full detail, but I was hoping if you had some suggestions how to better convey crowded areas full of colorful characters.