Encoding : Throughput & Quality equivalents

Throughput
As mentioned in the previous section, throughput is the measure of the amount of bandwidth you use over time. You'll encounter throughput when you use a service to distribute your podcast, because most offer a certain amount of throughput for free and bill you for any used in excess of that. Obviously, you want to keep your monthly bill as low as possible, so you want to try to limit the amount of throughput you use.

When you encode your podcast, you want to balance the desire to provide the highest quality possible with the reality of your throughput bill at the end of the month. Many podcast distribution services offer generous amounts of free throughput each month, so this may not be an issue when you first start out. If your podcast becomes wildly popular, though, you may be faced with a need to cut your operating costs (until that first sponsor or advertiser comes around, of course). If so, you may want to consider reducing the bit rate of your podcast, which reduces the quality of your podcast, but that may not be noticeable to your audience. Remember, most people listen to podcasts while sitting in front of their computers, and multimedia speakers aren't renowned for their quality. What you want to deliver is a podcast quality that is equivalent to other broadcast media, which in the case of AM and FM radio isn't that high to begin with.

Quality equivalents
The concept of broadcast quality to mean really, really good. However, anyone who has listened to AM radio knows that it doesn't sound anywhere near as good as FM, and for that matter FM radio doesn't sound as good as CDs. Yet they're both broadcast standards, and we still listen to radio, even AM. Different types of programming do not need as much fidelity as others.

The idea, then, is to figure out how much fidelity your programming requires and produce content to that standard. When recording the content, you should always record at a very high standard, because that gives you the most flexibility later on. But when it comes time to encode your content for Internet distribution, you may want to sacrifice a bit of quality for the cost savings it provides.

Table 1 lists some common bit rates offered by encoding software and brief descriptions of what quality you can expect using different encoding technologies.

Note In Table 1, you should notice that MP3 audio quality is always slightly worse than Windows Media, Real, and QuickTime AAC, particularly at low bit rates. This is because the MP3 codec is older and wasn't really designed for low bit rate encoding. At higher bit rates (128 Kbps and above), the quality differential is less apparent.