Korg SDD-3000 Owner's Manual page 18

milliseconds) with an 8 kHz response and a 24 kHz sample rate - all with the same amount of memory, 42 milliseconds
isn't very much time, but it's enough to do things like chorusing and flanging - although flanging with only an 8 kHz
response tends to sound muffled at best.
The Korg SDD-3000 Digital Delay uses the latest 64K RAM technology to provide over 65 thousand 'words' of
memory for a maximum delay time of 1023 milliseconds at full 17 kHz response. This extended delay time is a
standard feature - no additional expander board is required.
Clarity and the fine print
Good frequency response isn't the only important characteristic, of course - it's also necessary to reproduce sounds
cleanly, with a minimum of noise and distortion. Older tape and analog delay lines added undesirable noise and dis -
tortion making it almost impossible to get clean results, especially al long delay times and/or high Feedback settings.
Noise reduction or 'compander' techniques were added to the better analog delay units (as well as many digital units), in
order to keep noise down to reasonable levels. Unfortunately, you can usually hear side effects from the non studio-
quality noise reduction used in delay lines. One side effects is 'breathing', also called modulation noise, which is a
change in the background noise level when the signal level changes. Another undesirable side effect is a definite lack of
"punchiness", because noise reduction circuits generally use a compressor and this tends to take the sharp edges off of
percussive sounds.
A second problem is distortion.
Tape and analog delays produce many forms and distortion, which progressively degrade the sound. Digital delays
eliminate almost all of this distortion, but introduce two forms of their own. The first type is caused by putting
frequencies into the delay that are higher than half the sample rate (this is why it's better to sample at 3 times the
response limit, as mentioned above). This kind of distortion is called 'aliasing' or 'fold-over' distortion, and it puts a
very brittle, almost "ring-modulated" edge on the sound when it occurs.
The other type of distortion produced by digital units is called 'quantizing' distortion. It's related to the fact that digital
circuits turn sounds into numbers. This has a lot of advantages -numbers don't get any noisier or more distorted not
matter how long they're stored, unlike analog signals. However, distortion can happen when the sound is turned into a
number and back again. For example, if the circuit can handle numbers like 7, 8, 9. etc., but not anything like 7.2 or
8.65, then a audio signal with a value of 7.2 at a particular time will come out of the digital unit with a value of 7.0, and
a signal that should be 8.65 will com e out as 9.0. This is called 'quantizing' distortion because it occurs when a signal is
turned into a number, or 'quantity'. It Is a very definite, gritty-sounding kind of distortion, and it can only be avoided by
making sure that the 'spaces' between the numbers (resolution) are small enough that the distortion isn't audible. This
means that you have to have lots of 'bits' - the more bits, the more resolution and less distortion you have.
Having lots of bits helps with the noise problem too, because it not only improves the resolution of the numbers, it
also increases the range of numbers that can be handled. This directly increases the basic dynamic range and
signal/noise ratio of the system. Most digital systems use 8 - 11 bits plus noise reduction and get reasonably good
result. The Korg SDD-3000 uses 13 bits of information and special proprietary technology to provide exceptional sound
quality without any noise reduction circuitry and resulting undesirable side effects.
To summarise, the Key advantage of digital delays is that they turn sounds into numbers. This allows products to have
much better highs, noise and distortion than analog or tape units can provide. Moreover, since numbers don't care if
they get noisy the long delays and repeating echoes that drive analog and tape delays into nervous break downs aren't a
problem with digital units.
On with the show
Now that we have some of the technical stuff down, we can start talking about how it's all used to produce the different
effects.
A basic block diagram of a delay system is shown below (A complete block diagram of the SDD-3000 is included later
in this manual). It includes four important parts: 1) the delay line, 2) a way to vary or modulate the delay time, 3) a
balance control which mixes the delayed and direct (unprocessed) sounds, and 4) a way to add feedback or regeneration
around the delay line. The analog to digital and digital to analog converters are not shown to keep things simple.
[BLOCK DIAGRAM '1', attached.]