Dithering


Prepare studio-quality audio for CD and other formats with Ozone's essential dithering tools. Ozone allows you to effectively convert and dither to 24, 20, 16, 12 or 8 bits.

Key Features

   Includes iZotope MBIT+ Dither for exceptionally transparent conversion to different bit depths

   Unique set of bit scopes and DC level meters provides a complete view of the digital bitstream and conversion process

Note: Dither is independent of the Maximizer

To turn dithering on and off, change the Dither type. By default, the dither is off (Type "None"), meaning that your program material is left in the original format. To reduce the bit depth of the material, change the Type from None to MBIT+, Type 1 or Type 2.

When the Type is MBIT+, Type 1 or Type 2, dithering is applied and your audio will be reduced in bit depth to the number of bits selected in the Bit Depth control. The following options are available when reducing the bit depth of the audio.

Type

None: No dither or bit reduction is applied.

MBIT+: This is a proprietary iZotope word length reduction technology that reduces quantization distortion with minimal perceived noise. While this might sound like a paradox, MBIT+ is a very smooth, quiet and almost "analog sounding" technology.

Type 1: Dither is applied using a "rectangular" distribution function. While this provides a dither noise source with a low amplitude, the dither noise can become modulated by the audio signal and vary in level, which is undesirable in many situations. Also, the non-linear quantization distortion is not completely suppressed in some situations with this low dither amplitude.

Type 2: Dither is applied using a "triangular" distribution function. This dither is larger in amplitude and completely suppresses the non-linear quantization distortion.

Shape

By shaping the dither noise, it is possible to provide more effective and transparent dithering by shaping the dithered noise spectrum. There are several different methods for shaping noise so that it is less audible yet still effective. Please refer to our online mastering guide for more information as to the technology behind these methods and how to apply them effectively.

Type 1 or Type 2 Shapes

None: No noise shaping is applied

Simple: High pass filtering is applied to the dithered noise.

Clear: The noise is shifted towards the Nyquist frequency, near the upper limit of our hearing.

Psych 5: A fifth order psychoacoustic shaping is applied to provide dither across the spectrum. The shaping is designed to move the noise away from frequencies that are heard as "louder" at low levels.

Psych 9: A more complex ninth order psychoacoustic shaping is applied.

In general, the "Clear" option is a safe bet for complex program material, although auditioning the dither against the Psych 5 and Psych 9 shapes may be more desirable in some cases.

Note: Psych 5 and Psych 9 shapes are specifically designed to be used on audio with a 44.1 kHz sample rate. For other samples rates, use None, Simple or Clear shaping, or MBIT+ mode which is designed for effective word length reduction at any sampling rate.

MBIT+ Shaping

The MBIT+ dither technology also provides options for noise shaping. You can control the aggressiveness of this shaping, ranging from None (no shaping) through Ultra (roughly 14 dB of audible noise suppression). 

Bit Depth

This is the target bit depth for the audio. When mastering for a CD, for example, you would want this set to 16.

Note: Ozone does not perform the actual conversion of the audio. After processing a mix with Ozone, it is necessary to then actually convert the audio to the desired bit depth in the host application.

For example, if you have a 24-bit audio file, you can use Ozone to dither down to 16 bits. The remaining 8 bits are "padded" as zeros. Your file is still a 24-bit audio file, there's just not anything but zeros in the lowest 8 bits. So when you then convert to a 16-bit file in the host app, the 8 bits (that didn't have any audio in them) are discarded.

1. Do not perform any processing to the audio after it has been dithered with Ozone. You may perform level adjustment with the output gain sliders in Ozone (those come before the dither) but do not change any levels in the host app or with other plug-ins. Almost all host apps have their master faders after the effects slot, so any level adjustment in the host app will destroy the dither.

2. Do not put any plug-ins after Ozone if you are dithering with Ozone. The dither must be the last thing that touches the audio.

3. Turn off dithering in the host app. Basically, you just want to truncate (throw away) the bits, because they're just zero anyhow.

Num Bits or Dither Amount

This sets the number of bits or amount of dither that will be used for the dither source. For Type 1 and Type 2 dither, in most cases 1 bit will be sufficient, but in some situations the "over-dithering" obtained by setting Num Bits to 2 can be useful. In MBIT+ mode, the dithering amount can be varied from None (noise shaping only) to High. No dithering or Low dither amount can leave some non-linear quantization distortion or dither noise modulation, while higher settings completely eliminate the non-linear distortion at the expense of a slightly increased noise floor. In general, the Normal dither amount is a good choice. 

Auto-blanking

Selecting this option instructs Ozone to completely mute dither output (i.e. dither noise) when the input signal is completely silent (0 bits of audio) for at least 0.7 seconds.

Limit Peaks

Dither noise is random in nature and has a very low amplitude. However, after noise shaping, especially in aggressive dithering modes, the high-frequency dither noise is significantly amplified, and the overall dither signal can show spurious peaks up to -60 dB FS. If such high peaks are undesirable, you can enable the Limit Peaks option to effectively suppress the spurious peaks in the noise-shaped dither.

Suppress Harmonics

If, for some reason, any dithering noise is undesirable, simple truncation remains the only option. Truncation results in harmonic quantization distortion that adds overtones to the signal and distorts the timbre. In this case you can enable Suppress Harmonics option to slightly alter the truncation rules, moving the harmonic quantization distortion away from overtones of audible frequencies. This option doesn't create any random dithering noise floor. Instead it works more like truncation, but with better tonal quality in the resulting signal. This option is applicable only in the modes without dithering noise and without aggressive noise shaping.

Meters

Ozone Dithering module offers a DC Offset meter and a Bit Meter.

DC Offset

It is a good idea to filter out the DC offset from your input before dithering. Again, please refer to our online guide for the background behind this. If you are dithering, turn the DC Offset filter to On. If the button says "On" the DC offset filter is on.

Dithering Guide

If you are interested in getting some practical tips for using dithering, as well as some of the theory behind it, please check out the Ozone Dithering Guide.