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Sample rate

From: Digital Audio Principles

Video: Sample rate

The process of Converting Analog to Digital is one of the most important processes when it comes to working with digital audio. It's important to understand what goes into it, because you'll be making decisions about how analog is converted to digital in a lot of different situations. So I want to talk about how we do that, and what it actually is. To be able to take sound and use it in the computer or in the digital domain, we need to come up with numeric representations of those analog signals, or those electric signals that are moving through our cables and wires.

Sample rate

The process of Converting Analog to Digital is one of the most important processes when it comes to working with digital audio. It's important to understand what goes into it, because you'll be making decisions about how analog is converted to digital in a lot of different situations. So I want to talk about how we do that, and what it actually is. To be able to take sound and use it in the computer or in the digital domain, we need to come up with numeric representations of those analog signals, or those electric signals that are moving through our cables and wires.

So there are two sets of values that determine how accurate these representations are. Sample rate and bit depth. Let's take a look at sample rate first. Sample Rate is actually just what it sounds like. It's the rate of taking samples. It's the amount of samples we take per second, or there are a number of times each second, we look at a sound and take a measurement of that sound. So the number of times we're analyzing, or looking, and scrutinizing a sound to see what's actually there. Now a Sample is an individual piece of information.

So each time we look, we say, hey, what's there, how louder, what frequencies are there. Then we write it down in a little notebook, which becomes a digital piece of information. It's basically the process of coming up with the numeric representations of what exists. Sample rates comes into play, because how many times you look has a big effect on how accurately you see what you're looking at. Needless to say with audio, we need to take a lot of samples to get a pretty accurate picture. There are a lot of things going on there, a lot of changes.

So sample rates are expressed as a frequency of samples per second. So they're expressed in hertz. We take a lot of them. A sample rate of 44.1 kilohertz in one single second, we're taking a look and sampling that sound 44,100 times. So that's a lot of looks. So every time we take a look, we record a sample, which is more or less numerical data. That is digital information that our computers can read and understand. The higher that sample rate is the better the sound quality we'll have.

Let's take a look at a few examples. So Higher sample rates = greater accuracy. I've a couple of visuals here. This is a analog signal coming in. These little gray bars represent taking a sample. So this is our sample rate. So these red dots kind of represent what we're seeing. When we take that look or take a sample, this is what we find. We know that this wave is at this point, at this time. This wave is at this point, at this time. So you can see here we have a lower sample rate, and so you get fewer samples.

It's pretty obvious. Higher sample rate, more samples. So we're taking more looks, and getting more little bits of information, more little measurements, and more little numeric representations of what's happening here. So in the next slide, we'll connect those dots. You can see that if we connect the dots at the lower rate, we miss out on a fair amount of information involved in the slide. In this one, we really miss this whole big spike. We missed some of the peaks for sure. We get a lot of that kind of middle information, but we missed out on some of the real extreme things happening here.

With a Higher sample rate, we get a much more accurate representation of that analog sound. This is why higher sample rates are better. So as you would expect, the higher the sample rate, the more accurate the reproduction of the sound, which in a way of saying the better sound. So the higher the sample rate is the more accurate the analog to digital conversion will be. Here are a lot of the sample rates you'll come into contact with digital audio. From the lowest being 8 and right now the highest being 192. If you go and buy an audio CD at the store, it's going to come in at 44.1 kilohertz.

Now 44.1 is really considered the minimum sample rate required to achieve high-quality digital audio. We come to this rate as a result of the Nyquist theorem, which concludes that a sample rate should be at least twice as high as the highest frequency you're trying to record or sample. Since humans can hear up to 20 kilohertz, a sample rate of twice that or 40K is required. Now the reason we got up a little bit further to 44.1, gets a little bit technical. I'm not going to go into it in this title. But certainly if you want to find out more about it, you can look up the Nyquist Theorem.

Any sample rate lower than 44.1, you can usually detect degraded sound quality. We'll listen to a few examples. Rates higher than 44.1K such as 48, or 96, and 192 are used quite a bit now in digital audio. They provide some really excellent results. We'll talk a little bit more about kind of some of the trade-offs of using different rates. It's not as simple as just saying, well, let's use the best rate. There are a few things you need to take into account. We'll talk about that in just a little bit. So let's go ahead and check out a few examples of things at different sample rates.

We'll start with something at 44.1. (music playing) So you can hear that's pretty good quality. It's pretty even. And this is the standard, if you buy a CD in the store or something like that, this is what you hear. It's not the highest quality available. It's generally accepted as very, very suitable quality. Now let's check out something at a lower rate at 22. (music playing) So at 22, we're actually taking half as many samples. So we're getting half as much information.

And obviously, we're not going to have as accurate representation of the sound. Finally, let's check out one at 8K. (music playing) So hopefully, it's easy to hear that there is a big difference in the quality between 8K and 22, and even more of a difference between 8K and 44.1 kilohertz. So at 8K, we're taking more than five times fewer the number of samples than we are at 44.1 kilohertz. The sound is noticeably not as good.

So that's a quick look at sample rate. Next, we'll look at bit depth. Then we'll think about how when it combined with sample rate will affect the overall quality of our digital audio.

Show transcript

This video is part of

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Digital Audio Principles

110 video lessons · 26903 viewers

Dave Schroeder
Author

 
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  1. 50s
    1. Welcome
      50s
  2. 39m 10s
    1. What is sound?
      4m 15s
    2. Hertz and frequency response
      5m 34s
    3. Phase
      2m 39s
    4. Capturing audio
      3m 39s
    5. Sample rate
      6m 16s
    6. Bit depth
      9m 47s
    7. The waveform
      5m 3s
    8. Audio file formats
      1m 57s
  3. 7m 25s
    1. What is a digital audio workstation?
      2m 59s
    2. Typical DAW signal flow
      4m 26s
  4. 50m 33s
    1. What microphones do
      1m 57s
    2. Element types
      5m 0s
    3. Pickup patterns
      6m 51s
    4. Axis
      2m 52s
    5. Frequency response and the proximity effect
      5m 10s
    6. Phase issues
      1m 41s
    7. Microphone types
      8m 44s
    8. Miking vocals
      5m 39s
    9. Miking amplifiers
      2m 17s
    10. Miking drums
      10m 22s
  5. 16m 39s
    1. Cables and connectors overview
      2m 42s
    2. Balanced and unbalanced cables
      3m 19s
    3. Common cable types
      7m 13s
    4. Cable tips
      3m 25s
  6. 12m 16s
    1. What is an I/O device?
      1m 41s
    2. Analog to digital conversion
      3m 10s
    3. Tour of an audio interface
      4m 49s
    4. Interface considerations
      2m 36s
  7. 21m 5s
    1. What is a preamp?
      3m 21s
    2. Input levels
      5m 29s
    3. Padding
      2m 18s
    4. Phantom power
      2m 37s
    5. Phase reverse
      3m 4s
    6. Preamp demo
      4m 16s
  8. 12m 56s
    1. What is a mixer?
      5m 55s
    2. Input section
      1m 17s
    3. Channel strips
      3m 16s
    4. Master section
      2m 28s
  9. 18m 21s
    1. What is monitoring?
      2m 11s
    2. Speakers
      4m 47s
    3. Room considerations
      5m 43s
    4. Headphone types
      3m 50s
    5. Monitoring levels
      1m 50s
  10. 15m 23s
    1. What role do computers play?
      1m 36s
    2. Performance issues
      4m 11s
    3. Hard drives
      4m 38s
    4. Mechanical noise
      2m 10s
    5. Authorization
      2m 48s
  11. 6m 54s
    1. Planning for recording
      54s
    2. Doing a system check
      1m 26s
    3. Planning your inputs
      1m 42s
    4. The recording environment
      2m 52s
  12. 25m 52s
    1. Types of digital audio software
      38s
    2. Multi-track recorders/sequencers
      4m 56s
    3. Two-track recorders/waveform editors
      4m 55s
    4. Loop-based music production software
      5m 44s
    5. Plug-ins
      6m 56s
    6. Other varieties
      2m 43s
  13. 18m 59s
    1. Common components
      46s
    2. The transport
      2m 4s
    3. The toolbar
      3m 19s
    4. The Edit/Arrange window
      4m 42s
    5. The mixer
      5m 8s
    6. The file list
      3m 0s
  14. 19m 17s
    1. Setting up a session
      3m 30s
    2. Assigning inputs and getting signals
      3m 19s
    3. Input modes
      3m 28s
    4. Overdubbing and punching
      5m 14s
    5. Bouncing down
      3m 46s
  15. 19m 42s
    1. What is editing?
      1m 21s
    2. Waveforms
      2m 53s
    3. Making silent cuts and trims
      7m 1s
    4. Fades and automation
      8m 27s
  16. 1h 23m
    1. What are plug-ins?
      3m 0s
    2. Using plug-ins
      6m 11s
    3. EQs
      7m 4s
    4. Dynamics pt. 1: Compressors, limiters, expanders, and gates
      5m 40s
    5. Dynamics pt 2: Applying dynamic effects
      7m 2s
    6. Pitch shifting
      6m 14s
    7. Reverb
      9m 28s
    8. Echo and delay
      6m 23s
    9. Modulation effects: Phaser, flanger, and chorus
      9m 39s
    10. Sound tools pt. 1: About, gain, normalize
      7m 39s
    11. Sound tools pt. 2: Reverse and time compression/expansion
      6m 29s
    12. Sound tools pt. 3: Noise reducers, dither
      8m 11s
  17. 23m 43s
    1. What is MIDI?
      3m 6s
    2. Keyboard controllers
      1m 23s
    3. Computer-based virtual instruments
      1m 6s
    4. Control surfaces
      1m 6s
    5. Recording and editing MIDI
      12m 4s
    6. Virtual instruments
      4m 58s
  18. 27m 29s
    1. What is mixing?
      1m 54s
    2. Some common objectives
      3m 4s
    3. Some useful techniques
      5m 59s
    4. A quick mixing demo
      16m 32s
  19. 18m 48s
    1. What is mastering?
      2m 24s
    2. Sonic maximization
      9m 43s
    3. Final preparations and exporting
      6m 41s
  20. 13m 34s
    1. What is audio compression?
      2m 16s
    2. Popular formats
      2m 9s
    3. Bit rate, sample rate, and channels
      5m 42s
    4. Other adjustments and considerations
      3m 27s
  21. 15m 6s
    1. Essential gear
      7m 36s
    2. Voice recording setups
      1m 43s
    3. The voice production process
      5m 47s
  22. 10m 4s
    1. Analog vs. digital
      2m 48s
    2. Tube vs. solid state
      5m 6s
    3. The continual upgrade
      2m 10s
  23. 18s
    1. Goodbye
      18s

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