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Conference napalm::commusic_v1

Title:	* * Computer Music, MIDI, and Related Topics * *
Notice:	Conference has been write-locked. Use new version.
Moderator:	DYPSS1::SCHAFER

Created:	Thu Feb 20 1986
Last Modified:	Mon Aug 29 1994
Last Successful Update:	Fri Jun 06 1997
Number of topics:	2852
Total number of notes:	33157

276.0. "Questions on sampling.." by EKLV00::COLLINS (Steve Collins .. ) Thu Mar 20 1986 06:01

Could anyone explain these poins on sampling to me.

1.	On a sampling keyboard ,when a sound has been sampled in to
	memory at one frequency and is being played back at a different
	frequency does the duration of the sample vary with the note being
	played ?
	If so , this would surely be very unsatisfactory with note
	durations being doubled and halved only an octave away from the
	origeonal.

2.	I have heard that some machines use looping to extend the note .
	How is this achieved ? Also shurely the attack and decay parts of the 
	envelope of the origeonal sample would have to be extended in the 
	same way.This seems like a very complex process to me ?

3.	How does the keyboard allow for signals to be sampled at different
	pitches and be replayed on a correct musical scale ?
	Is there a prefered pitch at which samples are made ?

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276.2 My Fifth-of-a-Dozen's Worth ERLANG::FEHSKENS Thu Mar 20 1986 15:13 44

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276.2	My Fifth-of-a-Dozen's Worth	ERLANG::FEHSKENS		`Thu Mar 20 1986 15:13`	44
	(BTW, this is the third time I've tried to reply to this item and had my answer blown away by a network error. At least Notes-11 would leave you a .TMP file to recover with. Any suggestions? I can't find any help in the VAXNotes documentation) 1) Tom describes the simple answer. More resourceful samplers use the looping technique you ask about next to solve the problem of "played duration longer than sampled duration". The pitch is controlled by the effective rate at which the sample is read out; I say "effective" because it's usually easier to repeat or skip sample values than actually change the clock rate. Note that some samples should be played back at a fixed length independent of how long a key is held down - e.g., percussive sounds. 2) Again, more resourceful samplers use a more effective technique. Divide the sample into three phases - attack, sustain, release. When the key goes down, read out the attack phase. If the key goes up before you get to the end of the attack phase, go to the release phase. If you get to the end of the attack phase and the key is still down, read out the sustain phase. If the key goes up before you get to the end of the sustain phase, go to the release phase. If you get to the end of the sustain phase and the key is still down, go back to the beginning of the sustain phase. Repeat as necessary. Good samplers allow you to edit the sustain phase so the start and end points match up better. This way the looping is not egregiously obvious. They may also allow you to control the attack phase read rate as a function of key velocity or pitch, simulating "envelope time dynamics" and "envelope key follow". 3) You usually tell the sampler which key you want the sampled sound to correspond to. You can "tune" the entire instrument by changing the clock frequency a little. This means you can transpose down or up at sample time, if you want. I think sampling is still and "up-and-coming" technology. I think it shows most promise as a source of waveforms to which you can then apply the filtering and enveloping techniques developed to support subtractive synthesis. len.

    (BTW, this is the third time I've tried to reply to this item and
    had my answer blown away by a network error.  At least Notes-11
    would leave you a .TMP file to recover with.  Any suggestions? 
    I can't find any help in the VAXNotes documentation)
    
 1) Tom describes the simple answer.  More resourceful samplers use
    the looping technique you ask about next to solve the problem of
    "played duration longer than sampled duration".  The pitch is
    controlled by the effective rate at which the sample is read out;
    I say "effective" because it's usually easier to repeat or skip
    sample values than actually change the clock rate.  Note that some
    samples should be played back at a fixed length independent of how
    long a key is held down - e.g., percussive sounds.
    
 2) Again, more resourceful samplers use a more effective technique.
    Divide the sample into three phases - attack, sustain, release.
    When the key goes down, read out the attack phase.  If the key goes
    up before you get to the end of the attack phase, go to the release
    phase.  If you get to the end of the attack phase and the key is
    still down, read out the sustain phase.  If the key goes up before
    you get to the end of the sustain phase, go to the release phase.
    If you get to the end of the sustain phase and the key is still
    down, go back to the beginning of the sustain phase.  Repeat as
    necessary.
    
    Good samplers allow you to edit the sustain phase so the start and
    end points match up better.  This way the looping is not egregiously
    obvious.  They may also allow you to control the attack phase read
    rate as a function of key velocity or pitch, simulating "envelope
    time dynamics" and "envelope key follow".
    
 3) You usually tell the sampler which key you want the sampled sound
    to correspond to.  You can "tune" the entire instrument by changing
    the clock frequency a little.  This means you can transpose down
    or up at sample time, if you want.
    
    
    I think sampling is still and "up-and-coming" technology.  I think
    it shows most promise as a source of waveforms to which you can
    then apply the filtering and enveloping techniques developed to
    support subtractive synthesis.
    
    len.