The sound of dither

Dithering is about spreading errors out, so that they aren’t related to the sampled signal. A constant background hiss is easier to ignore than tones that change depending on signal frequencies and amplitude.

Here’s a fixed-frequency sine wave, truncated to seven bits:

7-bit sine tone, no dither

Here’s the same signal dithered, truncated to seven bits:

7-bit sine tone, dithered

Notice the problems with the non-dithered example, especially in the tail as the signal fades out and fewer bits are used.

Here’s a swept sine wave, first simply truncated to seven bits:

7-bit sine sweep, no dither

And again dithered:

7-bit sine sweep, dithered

Note the aliased frequencies in the non-dithered sweep, and how the tail sounds like a square wave as it fades out.

In both cases, the dithered signal maintains the sine tone throughout, at the expensive of added “hiss”.

There are things we can do to make the hiss less obtrusive, but of course at the more normal 16-bit sample size, the dither-noise level is far lower than these extreme examples.

Read the EarLevel article on dither.

This entry was posted in Digital Audio, Dither. Bookmark the permalink.

7 Responses to The sound of dither

  1. Bob L. Sturm says:

    Nice blog! I have added you to our blogroll. Keep up the nice examples.

  2. Doug Mann says:

    I’ve never thought about it before, but it makes perfect since to listen to dither at low bit depth. This certainly helped my understanding of dither. I’m a huge fan of your site, it is one of my favorite references.

  3. Richard says:

    Finally an excellent audio demonstration of why dithering is used. I’ve been dithering my final mixes at the last mastering stage on the basis that it was recommended by professionals. I knew that dithering had something to do with improving the “quality” of the final mastered audio but I couldn’t really “hear” why. With these audio examples you can actually hear the disturbance to the waveform in the tail of the non-dithered sine wave as it fades away. Thanks for this excellent explanation.

  4. Steve Kralik says:

    I heard 24 and 32-bit audio files do not require dithering, and if it’s added, it’s often inaudible. If that is the case, what’s the non-acoustic static I hear on virtually every purchased recording?

    Also, are there any songs (and I mean SONGS… purchasable complex audio) that demonstrate dithering or the lack there of audibly? If not, why are professional masters dithered?

    • Nigel Redmon says:

      There are many sources of noise in recording, but the most fundamental is thermal noise, either in electric and electronic instruments, or simply the recording path.

      Check out Perspective on dither for a more concrete idea of real distortion levels of non-dithered audio.

  5. Steve Kralik says:

    And for that matter, most professional music has dynamic range compression increasing the perceived volume, which means much of the data is above 1-bit, so it shouldn’t require much dithering (if at all)… right?

    • Nigel Redmon says:

      Right—the error is low level, so it would get masked by loud compressed music. It’s most easily heard on fades, sparse sections with exponential tails (held guitar acoustic guitar notes, for instance), and reverb tails.

Leave a Reply

Your email address will not be published. Required fields are marked *