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Understanding sample rate, bit depth, file formats, and dither

From: Mixing and Mastering with Pro Tools

Video: Understanding sample rate, bit depth, file formats, and dither

Part of the mastering process is eventually obtaining a stereo mix of your track in a format that is supported by mainstream playback systems. Now, whether that be a CD player, MP3 or other digital format, it is important to understand how digital audio is stored and ultimately the effect this has on the audio quality at the end of the day. So, in its uncompressed form inside of Pro Tools, digital audio exists as a finite series of discrete samples or frames where each sample is measured with a finite number of bits, ones or zeros, from the continuous analog waveform and this happens at the analog to digital converter stage.

Understanding sample rate, bit depth, file formats, and dither

Part of the mastering process is eventually obtaining a stereo mix of your track in a format that is supported by mainstream playback systems. Now, whether that be a CD player, MP3 or other digital format, it is important to understand how digital audio is stored and ultimately the effect this has on the audio quality at the end of the day. So, in its uncompressed form inside of Pro Tools, digital audio exists as a finite series of discrete samples or frames where each sample is measured with a finite number of bits, ones or zeros, from the continuous analog waveform and this happens at the analog to digital converter stage.

This sampling process is known as Linear Pulse Code Modulation and the data is most commonly stored in the WAV or AIFF file formats. So, an example would be audio recorded at 44,100 times per second or 44.1K at a resolution of 24-bits is measured 44,100 times per second or 44,100 frames with each frame or sample represented by 24-bits of data.

So, the sample rate is going to determine the maximum frequency oscillation that can be recognized by the system according to Nyquist and the bit-depth determines the quality or dynamic range that can be stored in each sample. So, this diagram shows you here on the x-axis. We are looking at samples and then the y-axis would be our bit-depth or the resolution available in each sample. So, generally when we record in Pro Tools, we like to record at higher sample rates in bit-depths to achieve maximum audio fidelity.

But because your average consumer playback system cannot read these formats, we must truncate and downsample our audio, throwing away some of the precision to comply with standards. So, for example, a CD is 16-bit, sampled at 44,100 times per second. So, despite all of this, it's still ideal to record at a higher sampling rate and bit-depth to maintain precision until the very last stage. Now, when this happens, inevitably, we have to truncate and some error occurs during the truncation, because we are going from a higher precision bit-depth to a lower precision, 24 to 16, the engineer is likely going to use dither to help alleviate some of the quantization error that occurs when moving to a lower bit-depth.

So, what happens is at the lower level, at the lower level details, error occurs when the specific amplitude of the waveform either triggers or doesn't trigger that least significant or that 16th bit, and at this low level, that error is actually correlated with the signal, or we get a correlated distortion that kind of sounds nasty on our low level amplitudes within our waveforms. Now, what dither does is it removes this distortion by adding some low level random noise, similar to wide noise and it's added at the truncation point or the least significant bit, the 16th bit in this case.

And this is effectively going to smooth out this quantization error associated with lopping off that lower 8-bits. So, if we look at this diagram, we are going to see that a low level sine wave at 24-bits, when truncated to 16- bits, we get a significant amount of quantization error. So, that is to say the difference between what the analog waveform would be and how it's digitally represented in each sample, there is a difference there and that difference is the quantization error.

By adding dither, we are actually able to smooth out this quantization error, this distortion. Dither is just sort of randomizing essentially what occurs at that least significant bit, so is it on or is it off. It's a randomization of this and humans are really good at actually hearing through this noise and pulling out the signal. So, what this allows us to do is effectively retain much more of our dynamic range, than if we were to just truncate at the 16th bit, without using the dither.

So, what are the rules for using dither in Pro Tools? Now, what I can do is if I'm balancing my mix internally and exporting it from the Region's list, dither is automatically added when I change the bit-depth here. It's just something that Pro Tools does behind the scenes. You don't have to worry about it. However, if you want to use your own special flavor of dither, which a lot of engineers, specifically master in engineers will do, what you need to do is apply it as the last plug-in on your Master Fader, so it needs to be the last thing in the chain.

Now POW-R dither comes with every Pro Tools systems and it actually has some noise shaping selections you could make. Now, noise-shape dither, instead of just being broadband noise, it actually pushes some of that noise into the higher frequencies that are less audible for humans, so it sort of optimizes the noise. You probably aren't going to be able to hear too many differences between the noise shaping types but the real audio file master in engineer types, you know, will swear by one noise shaping over another. Now, this is the last stage of my change and I don't want to change the volume after I hit the dither.

So, I don't want to raise or lower the level of the signal after it goes into the dither plug-in, because that will result in that noise, either being shifted up a bit or shifted down a bit, in a way that's not going to help us at all. So, I would use Bounce to > Disk in this case to perform a truncation down to 16 without Pro Tools adding any dither. So again, if you are going to use your own dither plug-in or if you are going to use the dither built into a brickwall limiter, some maxim has its own built in dither and in this case, I would not use POW-R dither.

So, if you are using the waves L2, L3 or some of these other brickwall limiters that have built in dither, you'll have that as the last plug-in in your chain and activate the dither on the plug- in and then use something like Bounce to > Disk. Now, if you still want to bounce your audio inside of Pro Tools into a new track and use your own flavor of dither, you have a few options. What you can do is you can export a 24 -bit version and then bring that into another program that allows you to add dither, so Bias Peak or Sound Forge or something like that or what you can do is just bounce it internally to a stereo track in Pro Tools and then add the dither to that track and then use the Bounce to > Disk engine to truncate down to 16-bits.

Now, ultimately the difference between bit-depths and sample rates may be very subtle and the differences in dither are even more subtle, but it's important to understand the role they play in mixing and ultimately, the mastering process, as your goal should be to retain every detail from your hard work during the mixing stage when the listener pops it into their CD player.

Show transcript

This video is part of

Image for Mixing and Mastering with Pro Tools
Mixing and Mastering with Pro Tools

77 video lessons · 9477 viewers

Brian Lee White
Author

 
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  1. 14m 50s
    1. Welcome
      1m 12s
    2. The past, present, and future of mixing
      6m 20s
    3. Strategies for mixing and mastering
      5m 38s
    4. Using the exercise files
      1m 40s
  2. 40m 24s
    1. Mixing "in the box"
      5m 9s
    2. Setting up the studio: Speakers and acoustics
      13m 12s
    3. Staying organized: Effectively prepping the mix
      10m 50s
    4. Managing system resources during mixdown
      11m 13s
  3. 41m 39s
    1. Introducing the Pro Tools Mixer
      2m 24s
    2. Understanding mixer signal flow
      3m 42s
    3. Using inserts and plug-ins
      7m 4s
    4. Working with plug-in settings
      5m 1s
    5. Using sends and creating FX returns
      6m 55s
    6. Submixing with aux tracks
      4m 30s
    7. Using groups while mixing
      3m 46s
    8. Using master faders effectively
      8m 17s
  4. 21m 11s
    1. Conceptualizing the mix and making a plan
      7m 45s
    2. Using volume and pan to balance the mix
      11m 18s
    3. Knowing when to process: Mix problems vs. mix solutions
      2m 8s
  5. 1h 3m
    1. Understanding the mechanics of sound
      3m 53s
    2. Learning the basics of EQ: Frequency-specific level control
      4m 29s
    3. Using DigiRack EQ III
      16m 3s
    4. EQ strategies in mixing: Corrective vs. creative
      7m 18s
    5. EQ workflow example 1: Kick drum
      5m 39s
    6. EQ workflow example 2: Filtering loops
      5m 10s
    7. EQ workflow example 3: The "telephone" effect
      3m 7s
    8. Mixing tips and tricks for EQ
      17m 36s
  6. 1h 15m
    1. Understanding dynamics and dynamic range
      2m 1s
    2. Working with dynamics processors
      2m 57s
    3. Using the DigiRack Dyn III compressor/limiter
      10m 6s
    4. Balancing and shaping track dynamics
      3m 19s
    5. Using gates and expanders
      9m 22s
    6. Using de-essers to eliminate sibilance
      5m 47s
    7. Dynamics workflow example 1: Vocals
      10m 0s
    8. Dynamics workflow example 2: Drums
      9m 29s
    9. Mixing tips and tricks: Dynamics
      11m 37s
    10. Building parallel or "upward" compression
      7m 53s
    11. Reviewing dynamics concerns: How much is too much?
      3m 28s
  7. 47m 48s
    1. Using time-based effects to add depth and width
      3m 22s
    2. Using DigiRack D-Verb
      14m 27s
    3. Using the DigiRack delays
      9m 18s
    4. Mixing with reverb
      7m 59s
    5. Mixing with delays
      6m 19s
    6. Mixing tips and tricks: Creating mix depth
      6m 23s
  8. 18m 8s
    1. Working with the Creative Collection
      9m 8s
    2. Building distortion and saturation
      9m 0s
  9. 37m 33s
    1. Understanding automation
      4m 10s
    2. Recording real-time automation moves
      7m 6s
    3. Viewing and editing automation
      10m 17s
    4. Automating plug-ins
      7m 36s
    5. Automation strategies for mixing
      8m 24s
  10. 29m 31s
    1. Understanding the characteristics of a great mix
      7m 2s
    2. Working to reference tracks
      4m 35s
    3. Avoiding some common pitfalls
      7m 50s
    4. Building healthy mixing habits
      3m 36s
    5. Crafting your mix from start to finish
      6m 28s
  11. 1h 5m
    1. Understanding mastering
      4m 15s
    2. Bouncing the mix
      7m 9s
    3. Working with general mastering strategies
      8m 50s
    4. Using limiting and compression to maximize track level
      10m 57s
    5. Working with multi-band compression
      7m 9s
    6. Understanding sample rate, bit depth, file formats, and dither
      7m 30s
    7. Using Pro Tools for CD track sequencing
      10m 11s
    8. Compressing audio for the web
      9m 41s
  12. 44m 51s
    1. Tips for evaluating plug-in processors
      6m 51s
    2. Using EQ plug-ins
      5m 35s
    3. Using dynamic compression plug-ins
      11m 3s
    4. Using reverb and delay plug-ins
      10m 46s
    5. Reviewing additional plug-ins
      10m 36s
  13. 57m 18s
    1. Effectively using saturation/analog style effects
      13m 40s
    2. Setting up side chains
      7m 5s
    3. Master buss processing
      5m 34s
    4. Creating and using mix templates
      6m 54s
    5. Surround mixing
      6m 22s
    6. Dealing with plug-in delay and latency
      6m 26s
    7. Drum sample replacing
      11m 17s
  14. 32s
    1. Goodbye
      32s

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