GamesRadar have managed to get themselves an audio Q&A with Matthew Smith, Craig Conner and Will Morton, three senior members of the Rockstar North Audio team.

The article talks about the ambient sounds in the game, pedestrian dialogue and the soundtrack of the game. There article is a pretty interesting read, here are some notable quotes from it:

• Most of the time what you hear is really happening - what’s so great about GTA IV from an audio team’s perspective is that you hardly ever need to fake anything – the world’s so rich and so busy, that if you make individual things sound right, the whole ambience pretty much just appears by itself.
  
• Gunfire is a good example of how complex videogame audio has become; a single gunshot typically consists of around 10 individual components, whose volume and placement we control independently with distance, to create a bright, wide, punchy sound up-close, and a more reverberant, muffled sound at a distance. For multiplayer, we balance this so that guns only really sound dangerously beefy when they’re at a distance you can be hit from, so it’s intuitive what’s threatening and what’s someone else’s private war.
  
• It’s difficult to quantify how many speaking parts there are, but at our last count there were over 740 unique voices in the game. There are over 80,000 individual lines of dialogue, more than 7000 of which are Niko’s lines. If you were to listen to each line back to back, it would take over 29 hours. Also, these figures don’t take the radio, TV, and mo-capped cut-scene dialogue into consideration.
  
• We also decided to make the pedestrian dialogue more realistic in GTA4. As an example, peds in previous games would walk around and randomly chat to themselves if they weren’t doing much else. In real life, people (generally!) don’t go around talking to themselves, so we dropped this behavior from GTA4. However, we realized that the random chat of old GTA games was a good way for the player to pick-up on what sort of personality a ped has, so we created the cell-phone conversations in GTA4 as one realistic way of portraying personality.
  
• The DJS have far more AI than previous titles. They know what time of day it is, what the weather is like and what’s going on in LC. They've even done their research on their playlists, some of their own tracks appears on them. In fact all the DJS are either famous singers or musicians (or both.) They have plenty to say about their chosen genre of music as they've lived it, loved it, or are living it.
  

The article also contains a number of brand new screenshots. You can see them over at GamesRadar.