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Understanding digital audio concepts

From: Soundbooth CS5 Essential Training

Video: Understanding digital audio concepts

When you hear audio, it's always analog. When you work with audio in Soundbooth, it's always digital. The difference is that analog sound consists of sound waves, continuous sound waves with variations of air pressure, whereas digital sound is just a bunch of numbers, numbers that when connected, approximate, closely approximate the original continuous sound wave. There was a time, not to long ago when all recordings were analog. Sound would hit a microphone, the diaphragm in the microphone would vibrate, and depending on the speed of the vibrations, it would send voltage changes to a recording device, like a magnetic recording device or a vinyl record where it would lay down continuous sound waves.

Understanding digital audio concepts

When you hear audio, it's always analog. When you work with audio in Soundbooth, it's always digital. The difference is that analog sound consists of sound waves, continuous sound waves with variations of air pressure, whereas digital sound is just a bunch of numbers, numbers that when connected, approximate, closely approximate the original continuous sound wave. There was a time, not to long ago when all recordings were analog. Sound would hit a microphone, the diaphragm in the microphone would vibrate, and depending on the speed of the vibrations, it would send voltage changes to a recording device, like a magnetic recording device or a vinyl record where it would lay down continuous sound waves.

Well these days, almost all recordings are digital. Analog sound is converted into samples, numbers that simply represent the amplitude, the volume level at that particular moment. Nothing in an individual number in the sample really equates to the original sound and to me, that's just mind boggling. Let me show you what I mean. So here is that a440 waveform that I have used in other movies, and you look at it and it looks a smooth, so called analog wave, the way you would expect sound to look if you could see it.

But in fact, it's not a smooth wave. It's a bunch of discrete numbers, little dots, little samples they call it. Let me zoom in on that. I will show you what I mean. I am just going to go a little bit at a time here and you will see that that the wave is going to start breaking up into little pieces. Each of those pieces is a sample. It's just a number, a number, in this case, that can range from around -32,000 up to about 32,000, a spread of about 65,000. So that's all these little samples are - just numbers. You can hear it, if you drag your cursor across it, because the folks who designed Soundbooth let you hear it, but otherwise this would just be a number and would not represent anything in terms of the quality of sound. But when you drag your current time indicator, it's actually sampling sound from both sides of that line and letting you hear it, that in fact, it's just the number that represents amplitude.

This number down here would be something less than zero because it's below the crossing point here, as I call it. This number over here, would be something greater than zero, representing an amplitude of higher pressure, lower pressure, higher pressure. And that's what all digital sound is is just a bunch of numbers, spaced out evenly over time, that represent amplitude. Let me show you something from the Help file that gives you a better indication of how that works. The Sample rate determines the frequency range that you can have for your sound and the sample rate that we are used to, mostly likely, is the CD Sample rate, which is 44,100 Hertz, 44,100 samples per second, uniformly spread out over time.

So, that means in one second, when you record audio, from analog audio to digital audio, it's sampled 44,100 times per second and you get 44,000 individual numbers that range from something high or something low, indicating the amplitude. And that 44,100 samples per second allows you to hear between zero waves per second to 22,050 waves per second, or Hertz as it's called. That's the frequency range of human hearing, basically, from 0 to 22,000. In fact, few humans can hear up to 22,000 cycles per second.

So, this gives you the full range humans can hear and that's why it was selected for CDs, for some other reasons as well, but this particular reason was that's within the human hearing range but the thing is at high frequency, the reproduction is not necessarily perfect and some audio folks might argue that point, but I will show you an example of what I mean later. But right down here, you notice that DVDs are up to 48,000 Hertz and high-end DVDs, like Blu-ray, can be up to 48,000 Hertz, which is way above human hearing, but what that means is at the peak of human range, around 20,000 Hertz, the quality of the audio there will be more accurate than the quality of audio is here at that range.

Let me go back to Soundbooth to show you what I mean. Now I am going to look out the whole view here. I want to go to this high frequency zone and move over there. Over here, the frequency is about 14,080 cycles per second, which is not 20,000 as I mentioned for the CDs, but it's approaching that. So, we have basically 14,000 or so waves per second that are being sampled at 44,000 samples per second. So, let's zoom in on that. I will keep on zooming in on it over here.

As I zoom in here, you can begin see the waveform. Now notice this is each sample, and there are about four samples per wave. So, how can it be that four numbers, it's all these that are numbers, can represent the entire waveform? And if I even raise the decibel level, which makes the amplitude much higher, it's still four samples in that little area. Yet somehow, they are now defining a louder tone at that frequency. And the way this works is when you change your digital audio to analog, when you change it from what you see on your screen to actually hearing it coming out of a loudspeaker, which is done using hardware or software called a digital to analog converter, it's taking each of these samples and analyzing what came before and what came after and filling in the gaps using interpolation.

It's not entirely accurate. Theoretically, it's accurate, but practically it can't completely, accurately reproduce the sound with only 44,000 samples per second, but it's pretty close. But you can see it's just the bunch of little numbers there. Let me talk about what those numbers represent. Those numbers have what's called a bit depth and for CD, that's 16 bits. That means 16 bits per number, which allows you have the number that ranges between 0 and 65,000, but in terms of audio, it's actually -32,000 something to -32,000 something because audio is high pressure and low pressure.

So, the range has as many as 65,000 different values, but if you want to have a higher amplitude, you want to have more decibel-range in your audio, you need to record your audio at a higher bit depth. So, the best bit depth, as you can see here in this little graphic from the Adobe Soundbooth Help file, shows you that at 32 bits, you have a range of 192 decibels, which is way, way beyond what humans would be willing to withstand. But 96 decibels is really not the full range of, let's say, a symphony orchestra, which has very, very quiet passages and then very, very loud passages.

So if you want to have that full range of recording and you are recording on something besides a CD, if you are going to output this thing to a DVD, for example, or Blu-ray, then you want to record it at higher bit depth so you will have a full dynamic range, each sample has a potential to have a much wider range of numbers so you have a greater dynamic range for your final output. Let me get back to one more thing. I want to show you the organ here. The organ is very complex. I'll zoom out a bit. Notice that the waves are very complex yet when these waves were sampled and converted into digital samples, they're still the same number of samples per second.

So, if I zoom in on this, you will see that even a complex waveform is made up only by these discrete little numbers, yet when they are played back, it plays back and sounds like the original organ. I don't think anybody could discern the difference at this 44,100 sample rate. (Organ playing.) So, that's basically how digital audio works. It's a collection of discrete numbers that represent only amplitude, but when you put them all together, it comes out sounding like the original sound.

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This video is part of

Image for Soundbooth CS5 Essential Training
Soundbooth CS5 Essential Training

52 video lessons · 14865 viewers

Jeff Sengstack
Author

 
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  1. 4m 51s
    1. Welcome
      1m 13s
    2. What is Soundbooth CS5?
      2m 30s
    3. Using the exercise files
      1m 8s
  2. 18m 4s
    1. Taking a look at basic sound waves
      3m 53s
    2. Taking a look at complex sound waves
      6m 43s
    3. Understanding digital audio concepts
      7m 28s
  3. 14m 45s
    1. Understanding the workflow
      5m 35s
    2. Touring the workspace
      3m 44s
    3. Customizing the workspace
      5m 26s
  4. 13m 11s
    1. Opening and importing files
      3m 59s
    2. Setting up recording hardware
      2m 35s
    3. Recording vocals and instruments
      6m 37s
  5. 1h 3m
    1. Playing and monitoring audio
      5m 10s
    2. Viewing audio waveforms and spectral displays
      6m 24s
    3. Selecting audio
      9m 14s
    4. Trimming and deleting audio
      3m 59s
    5. Copying, cutting, and pasting audio and inserting silence
      7m 55s
    6. Adjusting volume
      11m 21s
    7. Using specialized volume techniques
      6m 54s
    8. Creating and using loops
      4m 42s
    9. Stretching time and shifting pitch
      5m 14s
    10. Working with video files
      2m 22s
  6. 26m 50s
    1. Identifying noises: Hums, hisses, clicks, and pops
      5m 45s
    2. Removing background noise: Audio tape hiss
      7m 55s
    3. Removing vinyl record clicks and pops
      3m 57s
    4. Removing individual sounds
      9m 13s
  7. 13m 27s
    1. Previewing Soundbooth effects
      5m 32s
    2. Applying and adjusting standard effects
      4m 58s
    3. Applying and customizing advanced effects
      2m 57s
  8. 48m 25s
    1. Applying reverb and echo: Analog Delay and Convolution Reverb
      8m 46s
    2. Using delay-based effects: Chorus/Flanger and Phaser
      6m 8s
    3. Understanding sound-level effects: Compressor and Dynamics
      7m 0s
    4. Applying equalization effects: Graphic and Parametric
      11m 14s
    5. Exploring other special effects: Distortion and Vocal Enhancer
      7m 58s
    6. Setting the all-in-one effect: Mastering
      7m 19s
  9. 46m 42s
    1. Understanding multitrack concepts
      1m 16s
    2. Building a multitrack file
      7m 5s
    3. Adjusting track and clip volume and panning
      8m 54s
    4. Adding effects to individual tracks
      7m 38s
    5. Using Soundbooth sound effects in your multitrack file
      6m 38s
    6. Using three multitrack editing techniques: Duplicating, splitting, and cross-fading
      6m 15s
    7. Working with video in multitrack
      2m 49s
    8. Using professional production studio mixing techniques
      6m 7s
  10. 17m 13s
    1. Understanding how scores work
      3m 30s
    2. Previewing, downloading, and inserting scores into multitrack files
      4m 45s
    3. Adjusting score duration, intensity and parts
      8m 58s
  11. 10m 42s
    1. Dynamically linking to Premiere Pro and After Effects projects
      4m 31s
    2. Turning spoken dialogue into searchable metadata
      6m 11s
  12. 21m 42s
    1. Saving snapshots
      6m 23s
    2. Saving entire files or selected ranges
      11m 59s
    3. Saving and mixing down multitrack files
      3m 20s
  13. 10s
    1. Goodbye
      10s

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