Audio quality decreases when playing a game

Basic information:
Windows 8 x64
Latest version (2.0.3 - Just downloaded the exe yesterday)
Dell Inspiron 17R SE laptop
Using headphones (3.5mm jack)
Using internal mic (in the laptop - I’m using an external monitor so the laptop at the right side of the table → I’m not facing the mic)
IDT Audio driver A03 ( … 7r-se-7720)

I’m using Dxtory to record gameplay. I don’t care about the video, just about the audio. With Dxtory you can record multiple audio channels at the same time and later merge them (or not, if you want to edit them in audacity). This way I can record both in-game sounds and my voice and edit them separately.

Voice quality isn’t very good though. At first I thought it was because I am using the internal mic in my laptop that’s not even in front of me. So as a test I recorded my voice with Audacity (without playing a game)… and the quality was pretty good! Better than with Dxtory, at least. So then I thought it had something to do with Dxtory. So I started up a game and recorded my voice with both dxtory and audacity. Guess what, not only did the voice quality suck with dxtory (like it always has), now it also sucked with audacity. The only thing that had changed was that I was playing a game (and recording with dxtory at the same time).

Why can I record in good quality with Audacity when I’m not running a game and recording with Dxtory, and why does the quality get bad when I am playing a game and recording with Dxtory?

Thanks in advance!

Recording audio and/or video are quite demanding on parts of the system as they involve moving a lot of data around as continuous streams. This is particularly difficult for components such as hard drives and USB devices that only move data in one direction at a time. If there is a bottleneck that restricts the throughput of data, the quality will plummet and you can get all sorts of crackles, distortion and bits missing. To handle multiple media streams in real time you need to have an extremely fast and/or well optimised system. There are some optimisation tips in this article:
Also, running the game at a lower frame rate may help.