The frequency of the retrieval of a signal while conversion of the analogous signal into a digital one. A CD possesses the often named frequency of 44.1 KHz or 44100 Hz, for example.
ADC - "Analog to Digital Converter"
A component, which performs the conversion of an analogous signal to digital data. Its quality is mainly determined by sampling frequency and resolution.
These concepts mirror a split up of the behavior of a real instrument in order to be able to reproduce such a one in the world of synthesizers.
"Attack" stands for the attack of the Instrument - the part, where the sound reaches its maximum volume,
"Decay" for the time period of the sound reduction, until it meets with the pre-defined volume of the sustain,
"Sustain" is the time period, in which the sound remains at the same volume level,
"Release" determines the time period, in which the instrument fades out
While the sampling frequency represents the frequency of the signal retrieval, the resolution defines the fineness, in which the amplitude is measured.
Usual resolutions are 16 bits with the CD, while Dolby Digital (AC3) usually works with 18 bits and dts usually works with 20 bits. Highend sound cards even offer 24 bits meanwhile.
DAC - "Digital to Analog Converter"
Almost the same as the ADC, with the simple difference of reversed direction
In the beginnings of the computer time, a type of scene developed - people interested in computers, who understood something about hardware programming. In the beginning almost only active with Commodore machines, interest went over to the PC soon.
They had sat down with the goal to squeeze out the maximum from the existing hardware, and above all in Finland and round there are meetings and contests still today, in which people show their proficiency.
However, at the latest in '95 the actual hype eased, since almost everything was explored, that was to explore. Moreover the technology was so efficient meanwhile that it didn't represent any more big challenge.
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DSP - "Digital Signal Processor"
A processor specialized in a certain waveform, in our case for the processing of sound data. Note: In case of Creative Labs cards, "DSP" refers to "Digital Sound Processor", which names the custom programmed Intel MCS-51 family controller that is the heart of most Creative ISA cards.
The sound of a natural instrument consists, splitted into its components, of a main wave - the sound, which is the most evident - and several harmonic waves. The latter define the character of an instrument.
This theory was set up by John Chowning, student of the Stanford university, in the year 1972, and so many synthesizers of the company Yamaha do it in practice.
More on the history:
The of the Gravis Ultrasound and license products used DSP. It can mix up to 32 channels at a maximum of 44.1 Khz and 16 bits.
If digital information, because a sample should be played with half speed for example, is stretched, so a type of stairway effect originates. These stairways can be seen as a a small rectangle signal - at their edges emerge higher interfering frequencies, which are dependent from the actual frequency.
In order to counteract this effect, we calculate inter steps to fill the gaps produced by stretching, to minimize interferences. Hence an interpolated signal sounds essentially more natural.
The above displayed example only shows an ideal interpolation. However in reality, it rather looks like a point-to-point connection.
MIDI - "Musical Instrument Digital Interface"
Protocol, which was intended to record and return digital music on digital synthesizers. Initially, it was merely intended to interconnect two keyboards. However the technology was quickly adapted to computers.
The technology doesn't transport digital sample information, as for example PCM samples, but merely which instrument was used, in which pitch, how long it plays and the attack strenth etc.
Soon a standard called "General MIDI" established, which defined a standard set of instruments, primarily based upon Rolands own definitions.
Also coming from Roland, this is a MIDI interface grown to standard in the world of PC. If a software offers MIDI support, it will primarily support this standard.
In contrast to the possible channels, which a card can mix in hardware simultaneously, this explains the number of instruments, that a card can return simultaneously. This is to be explained the way that an instrument can take more than one channel to play.
The Yamaha OPL series are in versions 2 and 3 pure FM synthesizers, while version 4 already offered Wavetable synthesing. All models are downward compatible.
OPL2 offers mono sound with 6 to 9 voices and 2 operators, OPL3 already stereo with 20 voices and 4 operators maximum.
S/PDIF - "Sony/Philips Digital InterFace"
A standard that specifies the data exchange of digital sound data. Used in the beginning primarily for DAT recorders in order to avoid the detour over analog signals and hence to allow a copy reproduction bit by bit.
For MIDI playback used technology, so to speak the counterpart to FM synthesis. Real recorded instruments are stored in memory and are played slower of faster according to the wished pitch.
This technology could meanwhile oust FM synthesis considerable in the computer area.