Internal
The essential criteria for the power of a digital mixer are the number of channels that must be processed simultaneously, and the internal resolution. Example Digiface: 26 inputs plus 26 playback tracks can be mixed to 28 physical outputs in any order. This means (26 + 26) x 28 = 1456 combinations simultaneously possible. The mixer must be able to calculate 1456 channels!
As long as monitoring would have been the only point for this concept, one would have got away with 16 bit resolution. Including the playback tracks, this is no longer possible. Because they are always routed through the mixer, it does not only have to have higher resolution than 24 bit in order to avoid rounding errors for gain changes, but it also has to supply additional headroom for gain rises and the summing of several channels.
Extremely high resolution does not make sense and causes a high consumption of resources within the FPGA. We have therefore decided to have a basic fixed-point arithmetic with the following values:
The multiplier has 40 bit resolution. This comes from a maximum audio resolution of 24 bit, that can be altered in gain with a resolution of 16 bit (65563 steps) with a fader (24 + 16 = 40.)
The adder has 36 bit resolution. From these, 7 bit are used for the necessary headroom (up to 52 channels with 6 dB gain can be mixed to one channel.) The audio signal has again 24 bit resolution, the other 5 bit are used for the LSB to decrease rounding errors.
The output signal is truncated to 24 bit without dither.
Faders: 16 bit resolution, equals 65536 steps, which are provided following a special function for correct perception. Gain change input and playback channels: +6 dB down to maximum attenuation. Outputs: 0 dB down to maximum attenuation. Because of the screen display, the number of values that can be set with the mouse is dependant on the number of pixels. This is 137. In fine-mode (shift key), this value is multiplied by 8 for 1096 different gain values.
Pan: pan law 6 dB. This means, the signal is attenuated by 6 dB in center setting. From center to left and right, there are 50 steps on either side. Linearly processed and displayed, from L 1.00 via 0.50 © to R 1.00.
YoH,
а зачем по входу дитер добавлять? :huh: у нас же разрядность повышается...
[q]допустим на выход я могу поставить софтовый[/q] это как ты сможешь проделать?
