Meridian Audio Speaker manual Human-sized speakers

The Meridian Papers - 1 Meridian Loudspeakers: The DSP Path page 8

What is dither?

Why do we need it?

➤…Dither is not only required when a signal is converted between the analogue and digital domains: it is also needed any time a digital signal processing (DSP) operation is carried out, such as decoding a surround bitstream from a DVD, apply- ing a DSP preset, or passing through a digital tone control.

The more highly optimised the dither sig- nal, the higher the resolution – the further you can hear below the noise, and the more detail you can hear.

In a properly dithered system, the resolu- tion is effectively infinite.

Because you are nearer to the left speaker, the sound takes less time to travel from the speaker to your ears – and you are further from the right speaker, so the sound takes longer to arrive. Meridian’s approach to “bal- ance”, using the power of DSP, auto- matically adjusts these subtle time delays, so wherever you decide to sit, signals will arrive at the right time, as well as at the right level.

In addition, our processors can provide decoding using Trifield and Ambisonic technologies, which literally recreate a solid image of the original environment in your listening room – producing an incredibly lifelike surround-sound experi- ence, and even rotate the soundstage to suit where you are sitting.

Meridian’s DSP loudspeakers utilise 48- bit internal fixed-point resolution. This is a long way beyond what anyone can actually hear, but when you perform DSP operations, additional bits are creat- ed and it is vital that these are pre- served.

Furthermore, whenever digital signals are processed, they have to be dithered correctly.

Dither is a special form of noise that is added to a digital signal whenever oper- ations are performed on it. It smooths out imperfections and significantly improves the sound of a system. In fact, a properly optimized dither signal can make the resolution of a digital system effectively infinite (See sidebar, “What is Dither?”).

DSP technology is also used to provide additional features, such as tone con- trols and, because the loudspeaker knows the sound pressure level it is pro- ducing, loudness controls can be imple- mented more naturally than ever before.

The same principles can provide dynam- ic bass extension in smaller speakers,

where low frequencies are boosted more at low levels. The system com- putes cone movement, frequency and level, and as a result can provide bass protection, shutting down if there is a risk of parameters being exceeded. The voice coil temperature is also calculated, permitting precision thermal protection.

And finally, allowance can be calculated for different locations of the loudspeak- er in a room, such as boundary com- pensation when it is placed near a wall.

Digital signal processing also comes into play when you use a system at different levels. Our ears are less sensitive to bass and treble when we listen quietly: DSP can compensate for this according to carefully-research psychoacoustic princi- ples.

“Human-sized” speakers

Meridian’s speakers look, as well as sound, distinctive, and of course both these factors are related. It has been shown that loudspeakers that are as close to human-like as possible produce the best imaging – mirroring, in a sense, the position of human sense organs.

The “head” of a Meridian DSP loud- speaker (such as that of the DSP8000 shown above) produces the vast majori- ty of sound from 200 Hz up, which is where stereo and surround localization takes place.