Electronic musical instrument2009-10-12 00:00:00in the shift register for later reads by the CPU onthe CPU buss through buffer 215.
The DPC also has a duplicate of the sync counters
The DPC also has a duplicate of the sync counters contained in the PCC's and is able track of "dummy" partials by monitoring the global sync signal. This prevents spurious 1/10 transactions from being interpreted as valid partial data.
The one-bit modulo sum dither DAC is driven by modulo-sum dither logic imbedded in the DPC. This logic takes the unused four LSBs of the output sample and sends it to the modulo-sum accumulator, a four-bit accumulator operating at four times thesample clock rate. (See FIGS. 3-6). When the accumulators' carry out is set, corresponding to one LSB at the main DAC, the one-bit DAC is turned on. This causes the energy represented by the four LSBs to make its way into the final output.
This has the effect of decreasing the noise present in the audible portion of the spectrum while increasing it in the 20-40 KHz range, where it will be easily taken care of by the anti-imaging filter.
Referring now to FIG. 10 there is shown an embodiment of the invention comprising at 300, input means such as a keyboard, musical instrument digital interface or the like; at 302 a host processor incorporating a Motorola 68000 chip and relatedprogram ROM, RAM, timers and ROM for installed sounds (see FIG. 1) an interconnection device between the 16 bit bus and the 8 bit bus; at 304, 306, 308, 310, memory devices for, respectively, providing stored information of sine wave partials' phase(304), frequency (306), log of amplitude (308) and log of attack/decay rate data (310) in stored addresses corresponding (for 304 and 306) to eventual, log-sin, look-up table usage at ROM 322. The data output of 304 and 306 are added at 312, of 308 and310 at 314. The output of 312, processed via log-sin noise ROM 322, and 314 is added at 316 to provide a sum for inverse log, at ROM 324. A combinatorial logic unit is provided at 326 to control the address complementing unit (folder) 327 whichcomprements addresses for second and fourth quadrants of sine wave cycles but does no complementing for noise partials. The adding is done by summing gate arrays 312(A) and 314(B) and that sum is processed via similar gate array adders 316(C) and 318(D)to a digtial analog converter (DAC) 320. The adders (B) (C) are clipped at over/under range and modulo sum dither is applied to the end product (out of (D) analogously to the system described above for the FIGS. 1-10 embodiment; D's output modificationinvolves 1's complements adding. The form of clipping at (B) is sticking at max/min values while underflow is used at (C). The added sine wave partials converted to an analog output of the DAC is processed via conventional per se sample/hold (S/H),filter (FLTR), buffer (BF) equipment to headphone or other terminals (TL) and amplifier (AMP) and/or speaker (SPKR) components.
The logarithmic information is stored in a base-2 log convention to match oscillator frequency, sound range and computational needs.
While the above structure comprises the sound system for numerous voices, piano range is significantly provided with 32 kilobytes of stored information, compared to multi-megabyte order of magnitude storage for other synthesizers.
Piano-like random noise is imposed by a noise ROM 322 comprising two
interleafed spectral sets of random noise; each set may be associated, selectively, with a particular partial. The noise spectra are originally obtained as random number sets. Fourier transforms are obtained, modi...
