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AM and FM Defined
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The terms “AM” and “FM” are analogous to “AM” and “FM” radio. Like with a normal radio, the audio quality of an FM station sounds far better than an AM station. The same is true here. You can think of “AM/FM” to be the same as saying “lo/hi” quality.
Our original encoding standard was established in 2000; a time when dial-up Internet access was common. For that reason, our original encoding standard was established to meet the resources of the masses. This standard, now known as the “AM” standard, had a bitrate of 16Kbps with a sampling frequency of 11Khz.
Obviously, the audio was not that great, but for dial-up users, it was low enough to allow a listener to tune in and surf the web at the same time without any annoying pauses. The audio quality was an acceptable compromise between bandwidth and performance and served us well.
As broadband became more commonplace, the demand for something better became prominent. As a result, a new encoding standard was established in 2004 to address the demands for better audio. The mp3Pro encoding format was selected due to its ability to deliver the MP3 audio at half the bitrate. Now, let’s look at the math.
It is widely regarded that an MP3 encoded in stereo at 128Kbps with a sampling rate of 44Khz to have CD-quality sound. Using the mp3Pro codec, the same quality audio can be had at 64Kbps! This includes having dual channel (stereo) sound at a 44Khz-sampling rate! Stripping away an audio channel yields the same great audio quality, but with a bitrate of only 32 Kbps. At this setting, (mono audio at a high sampling rate, namely 44Khz,) the audio quality is comparable to FM radio.
The bitrate of 32Kbps was chosen because it yielded FM quality audio at a bitrate that would allow us to grow without severely taxing our system. Not only that, the bitrate is still surprisingly low enough to allow most dial-up listeners to tune-in to the improved audio format. And thus, the FM audio standard was born.
Originally, we were going to dump the old AM audio standard entirely, but because so much work went into creating a database of AM-quality audio, it was spared the axe and reused as a “low quality” or “AM” alternative for people on dial-up.
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