lp102918@sjuvax.UUCP (03/19/86)
...I know this is gonna sound like a stupid question,but hey!!!,
stupidity is a virtue.What is *digital* about digital delays??
Do they sample the delayed signal,or use microprocessors
to control feedback,or both??...
...also,why has mechanical (ie. spring-controlled) reverb died??
Was it particularly prone to failure? I have a Fender-Twin (circa.
'69) with mechanical that doesn't work,but when it did I thought
it was *fantastic*,super-genuine!!...
Larry Palena
PS- ...and what exactly *was* the story behind net.music.guitar??kirsch@sjuvax.UUCP (03/21/86)
In article <2920@sjuvax.UUCP> lp102918@sjuvax.UUCP (Larry Palena) writes: > > ...I know this is gonna sound like a stupid question,but hey!!!, > stupidity is a virtue.What is *digital* about digital delays?? > Do they sample the delayed signal,or use microprocessors > to control feedback,or both??... > > ...also,why has mechanical (ie. spring-controlled) reverb died?? > Was it particularly prone to failure? I have a Fender-Twin (circa. > '69) with mechanical that doesn't work,but when it did I thought > it was *fantastic*,super-genuine!!... > > Larry Palena > > PS- ...and what exactly *was* the story behind net.music.guitar?? > Larry, I think the big advantage to the digital reverb is the cleaner sound. Some people don't like the extra bit of treble/tinniness that you get from the spring reverb. I guess it's the same as all other analog vs. digital arguments--with the digital you can get a cleaner sound--which really gets some people off-though others still like the analog sound. -- "Honesty Ain't All that Hard, Just Put Rambo Back Inside your Pants" -Jello Biafra Paul Kirsch St. Joseph's University Philadelphia, Pa { astrovax | allegra | bpa | burdvax } !sjuvax!kirsch
etan@tellab1.UUCP (Nate Stelton) (03/24/86)
In article <2920@sjuvax.UUCP> lp102918@sjuvax.UUCP (Larry Palena) writes: > ...I know this is gonna sound like a stupid question,but hey!!!, > stupidity is a virtue.What is *digital* about digital delays?? > Do they sample the delayed signal,or use microprocessors > to control feedback,or both??... I'm no expert, but my understanding of DDL's is that the sound is sampled much the same way that digital recorders, digital phone lines, and sampling keyboards perform this task. The information is stored in RAM, and released at the end of it's sample duration (set by the 'delay' knob). DDL's are functionally the same as an echoplex. I believe microprocessors are used to control the management of the memory in terms of how long to sample, when to write over what parts of memory, and more recently, extensive MIDI and user interface. > ...also,why has mechanical (ie. spring-controlled) reverb died?? > Was it particularly prone to failure? I have a Fender-Twin (circa. > '69) with mechanical that doesn't work,but when it did I thought > it was *fantastic*,super-genuine!!... I wouldn't say it's died yet, but eventually... The main problems with spring reverbs are the "boing" (try mixing drum tracks through one), and the physical sensitivity (don't bump it with the amp cranked, and don't drop it while moving the equipment). As far as mechanical reverbs go, plate reverbs out-perform the springs for sound quality, but they haven't figured out how to put them in guitar amps yet. I am curious about how digital reverbs work. how do they produce the smear? How many samples are taken, played back, and heard at a given point in time? Anyone care to expound? -etan
greg@utcsri.UUCP (Gregory Smith) (03/27/86)
There are 3 basic types of reverb that I know of (1) mechanical (2) digital
(3) analogue
(1) Is the old spring-reverb that goes 'Pow' when you bump your amp - just
a bunch of springs stretched between two bars with a tiny 'speaker' thing
at one end and a mike-thing at the other. Different sized springs are
used in the same unit to avoid strong resonances. There is also a 'plate'
reverb - using a large metal plate instead of springs - that I have
heard of. It apparently sounds much better but its size and cost limit
its use to large studios.
(2) Digital reverbs. As has been said, these 'sample' the incoming sound,
store it in RAM, and haul it out later to be converted back to audio.
To get a better reverb sound (rather than a clean echo ) some other
things are done. First, the delayed sound is re-mixed with the incoming
sound to get regeneration. Second, the delayed sound is actually
'smeared' to get a less 'wired' sound. Suppose d(10) means 10ms-old
sound. Then a 10-ms delay might actually be done by:
delayed signal = .1*d(9.5) + .2*d(9.8) + .4*d(10) + .2*d(10.2) + .1*d(10.5)
I think more than 5 'taps' need to be used in practice, though.
Thirdly, the regenerated ( fed-back ) sound can be filtered, so
that the sound becomes 'duller' as it fades out ( or whatever effect
you want). Of course, the 'smearing' is in effect a digital filter,
as z-transform buffs will recognize.
(3) Analogue reverbs use CCD's - charge-coupled devices, also known as
'Bucket-Brigade' devices. This is an integrated circuit with a long
line of 'charge buckets'. A clock signal causes each bucket to be
emptied into the next, so that the charges in the buckets propogate
along the line. The charges are created at the input end in such a
way that the amount of charge in each created bucket is proportional
to the input signal at the time of creation. This charge will later
show up at the output end, and be transformed into a signal again
( sorry if this isn't very clear - I need pictures :-) ).
Thus the signal is still *sampled*, but the samples are stored as
charges instead of a memory word. The same things can be done here
as with the digital delay - the output can be fed back, and the
delay can be 'smeared' by using several taps near the end of the
delay line and mixing them. This type of reverb is cheaper than an
equivalent digital delay, but in general much less versatile. Also,
charges will 'leak' as they pass along the line, resulting in a
noise level much higher than that possible with a digital unit.
--
"No eternal reward will forgive us now for wasting the dawn" -J. Morrison
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Greg Smith University of Toronto ..!decvax!utzoo!utcsri!greg