SADiE's HiDither 96 noise-shaping dither plug-in offers 5 different noise shape types, two of which are optimised for 96KHz audio material. The other three are designed for 48KHz & 44.1KHz audio. Additionally Shape 1 is designed for use with emphasis.
Why noise shaping?
When a signal is quantised some of the detail within the signal is discarded and as a result an error is introduced. This error can be heard as noise and is correlated to the input of the quantiser. The noise signal can be very noticeable to a listener if the original signal is simple or of a low level. It is therefore desirable to try and reduce this correlation and subsequently produce a random noise signal. The use of dither does just that. It linearises the non-linear transform characteristic of a quantiser and reduces the harmonic distortion for low level signals. To summarise, the use of dither has two effects on the input signal to a quantiser; firstly it reduces the correlation between the noise and the input signal, and secondly it increases the total noise in the system. In essence, dither is a low level additive signal that causes the quantised signal to jump randomly between quantisation levels, which when averaged by the ear forms a smooth transition between the levels.
As the noise level has been raised by the addition of a dither signal, it is desirable to try and shape the noise to reduce the overall audible effect. Noise shaping filters are used to match the curve of the noise signal to that of the frequency response of the human ear. This reduces the noise signal where the ear is most sensitive, (between 1kHz and 8kHz) and increases the noise where the ear is less sensitive, (above about 14kHz) . An average response is taken for the human ear and so the effect of noise shaping will be slightly different for each listener. When using a high sample rate, for example 96kHz, it is possible to keep the noise floor lower for most of the human hearing range and move most of the noise signal to frequencies that are completely inaudible.
HiDither 96 is a cost option plug-in - contact your dealer for details of how to obtain it.