Data Compression: Advantages of Mono
sound that is directed through two or more speakers so that it seems to surround the listener and to come from more than one source; stereophonic sound.
Most listeners think of stereo as an improvement over monophonic sound, but there are many instances where stereo audio comes at a disadvantage. Podcasts, vlogs, interviews, or other audio content consisting mostly of dialogue sound best in mono. Rarely, if ever, do audiences benefit from hearing vocals panned left and right in the stereo field. In fact, if a listener has their left and right speakers placed ten feet apart, or if listening through one earbud instead of two, then the listener may actually lose information. Further still, true stereo sound requires the use of two or more microphones, or a “stereo microphone” with two microphone elements housed inside of a single capsule.
The Phantom Center
If a listener sits exactly between two stereo speakers, a psychoacoustic effect occurs whereby sound seems to originate in between the two speakers. For this reason, the vast majority of vocals in interviews, cinema, and television are kept in the center of the stereo field. Audio files can carry two identical mono channels into a single stereo file, or carry a single channel in a mono file. A mono audio recording played in a stereo system will behave identically, whether it’s encoded in stereo or in mono.
Stereo by Default
Stereo happens to sound great for music, but not so much for spoken words and dialogue. You can observe this by listening to an FM radio broadcast in your car during a commercial or DJ announcement. Notice how all of the dialogue seems to originate from the center, whereas the music contains elements placed left and right in the stereo field. Stereo comes in handy for any program material with large amounts of stereo content, such as an FM radio station. Stereo is less suited for content containing only mono sources, such as a speech, interview, or podcast.
When To Go Full Mono
If your content contains 90% or more of talking or dialogue, it’s wise to export the entire audio project into mono for simplicity’s sake. If your podcast includes music, ask yourself if your listeners truly need to hear stereo music for sixty seconds for a program that’s one hour in length. It’s more efficient to save the extra data from the second channel by exporting in mono and maximizing the amount of data allocated to that single channel used in the recording. This comes with some improvements, especially since web videos and podcast streams squeeze as much data as possible into highly compressed streams. Including an additional channel that rarely get used, if at all, only includes redundant data and slightly lowers audio quality.
Do the Math
Consider exporting a stereo file for a podcast at 96 kbps. This file splits the recording into two channels, allocating a very low 48 kbps per channel. Export the same file in mono and the entire 96 kbps are dedicated to the single channel at double the previous bitrate. That single audio channel containing double the information should sound better than the stereo audio file. It would be the equivalent of a left or right channel from a stereo recording encoded at a respectable 192 kbps.
Decades ago, software engineers devised a clever trick to allocate the maximum amount of data into a stereo file. “Joint Stereo” mp3s save space by either reducing certain frequencies to mono or by summing differences between the left and right channels. This can result in some minor audible artifacts, but it generally works well for highly compressed stereo sources. If discrepancies exist between the left and right channel, the resulting file might be larger than if it were mono. When exporting audio with large amounts of stereo content, encode with joint stereo.
In just about all other cases except cinema and music, panning vocals are seen a faux pas in professional audio production. Moreover, audiences stand to lose information if vocals aren’t kept in the center, or simply exported in mono. Save data and increase audio fidelity by exporting mono files for spoken dialogue, interviews, podcasts, or anything else with very little or no music.
Do you have any experience with exporting files in either mono or stereo? Did you notice a difference in audio quality or file size from either? Let us know in the comments below.