Attack of the Pod Penguins 3: Sampling, quality, and bitrates

Last month, we described the open source audio editing application Audacity as the 16-ounce framing hammer of podcast creation and editing. This month, we'll take a deeper look into Audacity, familiarizing you a bit more with the interface and some of the more esoteric but useful features of the application.

Let's start by setting up the application to meet your needs. From the menu, select Edit Preferences. You'll find a window tabbed along the left edge, full of options to tweak Audacity. Let's walk through the critical items tab by tab.

Audio I/O describes the input and output of the Audacity application, beginning with the sound device from which Audacity will capture audio. In most cases, this will be /dev/dsp in Linux, though your system may vary. You'll note, too, that the I/O tab includes both recording and playback - yes, input and output.

You'll also find a drop-down to select the output format: stereo or mono. When opening a new file in Audacity, this selection is used as the default. If you're recording a podcast that's primarily voice, mono should be your choice, if your voice will be the only one in the audio. You can select stereo if the podcast will be primarily music recorded directly to Audacity from a media player, and if your sound card supports stereo in. (Mixing and imaging multiple voices is best accomplished in hardware, something we'll discuss in an upcoming stories in the series.)

Finally, the Audio I/O preferences tab allows you to make a couple of important choices. The first, "Play other tracks while recording new one," allows you to create multitracked recordings on the fly, or, to mix musical cuts on the fly. If you have a good plan for your podcast episodes, this can save considerable time. Without the planning, though, you'll face a train wreck in trying to keep up with multiple musical selections when this option is checked.

The last option is very useful. "Software Playthrough" allows you to monitor your recording in real time. This is a great feature for all types of podcasts, but may require a high amount of processing power. It's especially useful if you're doing some hardware processing just before sending the signal off to the sound card. The feature allows you to hear what the sound card is hearing, as it's hearing it. I can tell you firsthand that what you hear through the monitor output of a mixer may not even come close to approximating what you'll hear in the recorded audio. This feature prevents those surprises.

The next tab in the preferences window is the Quality tab - another important tab for any podcaster. It sets the sampling rate at 44100 by default, the sample format as a high precision 32-bit float by default, and the sample rate conversion. The latter determines the method by which the software will interpolate the gaps between the samples. In other words, if your sampling rate is 44100, you'll have 44,100 digital samples of the source sound per second. But, that's only a sample of the original source sound, not a constant stream. Interpolation defines the method by which the software will make an educated guess as to what the other 43,999 gaps per second contain. While it may be hard to believe that these gaps are noticeable, a digital recording without interpolation has a harsher, less realistic sound.