Bits: A guide for the digitally challenged among us.
What the hell is bitrate and bit depth and why should I care? From the 30,000-foot view, most of us creatives don’t need to know these specifics, but in the digital world we operate in, a general knowledge is not a bad thing. At least you can feign some reasonable retort when that snooty audio technician asks do you want to record at 44K or 48K.
One definition of bitrate is the rate at which digital information can be transferred from one location to another. In this most general sense, it measures how much data is transmitted in a given amount of time, typically one second. It is expressed as kilobits,(Kbps)1,000 bits per second or megabits,(Mbps) million bits per second. For example, your home DSL connection may be able to download your favorite movie at 700 Kbps, but your cable connection may be able to reach 10 Mbps while the new fiber systems can easily reach 700 to 900 Mbps. There are real differences that can affect your distribution. If you have a big video file to upload to a client, there can be real time consequences for a slow connection at your favorite post house.
Bitrate can also describe the quality of an audio or video file. For example, an MP3 audio file that is recorded at 192 Kbps will have a greater dynamic range and may sound slightly better than the same audio file recorded at 128 Kbps. This is because more bits (samples) are used to represent the audio data for each second of playback. An easy analogy is that if you slice a cake in 8 pieces or samples, you are not going to see as much detail as if you divided that same cake in 16 pieces or samples. A video file that is recorded at 3000 Kbps will look better than the same file recorded at 1000 Kbps. Just like the quality of a still or video image is measured in resolution, the quality of an audio or video file is measured by the bitrate. This could explain a major difference between two cameras that both claim to be high definition. While they both may be recording 1080 lines of vertical resolution, one has decidedly more information because it is working at a higher bitrate. That’s one of the many reasons two cameras that record HD can have a cost differential of thousands of dollars. All else being equal, there will be an image quality difference corresponding to the difference in recording rate.
Some people will also talk audio bit depth. For most of us this is really getting too far into the weeds. Suffice to say, bit depth is the actual number of pieces of information for each of the above samples. It is another way of expressing audio resolution. For example, an audio CD employees 16 bits per sample while a DVD and Blu-ray disc can support up to 24 bits per sample. Using the above cake reference, one cake could be three layers deep, another eight layers deep. No taste guarantees, but I’m going to go for the eight-layer one.