When it comes to video, we need to deal with image size, aspect ratio, zoom settings, aperture, and frame rate. There are also numbers on the audio side, but they are easier to understand.
Isn't all audio digital these days?
In the past, audio was recorded on analog tape. For the end user, this was not much more difficult than today's digital voice recorders, but the behind-the-scenes work was much more complicated. For example, in the past, the average recording studio would hire an engineer to maintain the audio equipment. Before each recording, you must align the magnetic head, adjust the recording bias, and calibrate the level. If the studio or producer changes the brand or grade of the tape, a completely new setup will be required. In addition, the noise reduction system also brings its own calibration and artificial traces. Most importantly, the recording engineer must know how to record the tape in a specific way so that it sounds correct when played back. This pain and suffering continues to this day, especially in high-end studios who want the elusive "analog sound" of modern recordings.
For simple digital recording, we plug the audio interface into the computer, launch the recording app, check the volume meter, and click "record". Before post-production, we only need to make basic level adjustments. When using a camera to record audio, it's even simpler. Just plug in the microphone and click "Record" and the camera will do the rest. Of course, as with analog technology, there is a lot of work to be done under the surface of digital technology, but it is all done by the microprocessor. We just let them do their thing.
When audio enters a digital recorder or camcorder, the audio is digitized and converted into digital "text," which is then copied to tape, hard disk, or memory card. During playback, the digital stream is decoded and converted back into an analog signal, which is played back through speakers or headphones. Simple, right?
Digital audio sample rate
Once the audio is digitized, it has two specific characteristics: sample rate and bit depth. Sample rate refers to the number of samples per second when converting audio to a digital file. The more samples per second, the better the quality. The actual number of samples required to create a theoretically perfect copy is determined by the Nyquist-Shannon sampling theorem. The math can make you dizzy, so we can think of it this way: the sampling rate must be at least twice the recording frequency. For example, if you're recording an instrument like percussion, cymbals, etc., the recorded frequency and its harmonics can easily reach 20,000 Hz. This means that the sample rate required to recreate an accurate copy is 40,000 Hz. If you're paying attention, you'll know that CD audio specs require a sample rate of 44,100Hz, while DV video uses a sample rate of 48,000Hz. This leaves plenty of wiggle room for high-end sampling rates. Math nerds, feel free to look it all up on Wikipedia. This should keep you busy for a while.
The DV audio specification actually requires two sample rates: 48kHz and 32kHz. The 48kHz (often referred to as 16-bit) setting is the standard for two-channel or stereo recording. The 32kHz (often referred to as 12-bit) version can also record stereo sound, but it is also possible to record four-channel audio simultaneously on some cameras. The Canon XL2 is the first camera of this type that comes to my mind. The sample rate of 32kHz means that the highest frequency for recording audio is 16,000Hz, which is no problem for conversations and other tasks. If the sample rate of 44,100Hz and higher is called CD quality, then the setting of 32,000Hz is FM broadcast quality. It is suitable for casual use, but it is not recommended for critical applications. Curiously, many cameras, while not actually recording four channels, default to a 32kHz audio setting.
Bit depth
The explanation of bit depth is more complicated, so let's make an analogy first. In digital imaging, there are three common bit depths: 8-bit, 16-bit, and 24-bit. There are only 256 colors for 8-bit images. While you may never notice these limitations in cartoon images, an 8-bit sunset can look very strange. Due to the limited color, a large number of bands appear in the gradient from the horizon to the sky. The 16-bit image has a slightly larger color range, 65,536 colors to be exact. This provides more than enough options for making convincing images, especially on small screens such as mobile phones or handheld games. But check your digital sunset and you'll still see some strips, just not as noticeable as the 8-bit version. In digital imaging, 24-bit is often referred to as true color because it provides 16,777,216 colors. The 24-bit image covers most of the colors seen by the human eye. Digital cameras, both still and video, produce 24-bit images, and we're all very happy with the results.
Continuing with the analogy of digital photos, let's think about audio. Each digital audio sample is essentially a snapshot of the audio at the time. As you can imagine, an 8-bit sample with only 256 audio "colors" can be a bit grainy, and you're right. 16-bit sampling, on the other hand, has a greater range and produces a very reasonable version of the audio. That's why it's the standard bit depth for DVDs, DVDs, and audio CDs. The advantage of 24-bit recording is that each sample can produce more than 16.7 million audio "colors". While you won't use them on a standard DVD or music CD, the Blu-ray disc format supports 24-bit audio in various formats.
Next, multiply the bit depth by the sample rate. Now, you have an idea of the potential quality of your recordings. A typical DV or DVD audio soundtrack has a bit depth of 16 and a sample rate of 48kHz. As a result, 48,000 times per second of audio is digitized at 16-bit depth. The resulting sound quality is very pure and the original sound source is accurately reproduced.
You don't need to worry too much about sample rate or bit depth. Your device will automatically fix most of the problems for you. However, now that you know what these numbers mean, you can easily make a quick visual inspection when shooting video or recording audio. If the camera shows a recording frequency of 32kHz, change it before shooting. If you know how to use the 16-bit 48kHz setup on the audio interface, then setting up a voiceover session will be easier. In addition, you can post a status on Facebook saying that you are thinking about Nyquist's theorem and that your friends will think you are smart.
In professional recording studios, they usually record audio in 96/24 format. This means a 24-bit depth with a sample rate of 96kHz. Why is it so high? The 24-bit depth allows for amazing dynamic range and "color" possibilities. Engineers and producers love the 96kHz sample rate because it gives the recording more room to breathe or "air." Of course, when the CD is released, the final product is resampled to 44,100Hz at 16-bit. You can't hear the difference on an iPod, but in the studio, the improvement is noticeable. This results in a better original recording and is expected to reach a level of quality that will stand the test of time.
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