<HTML><BODY style="word-wrap: break-word; -khtml-nbsp-mode: space; -khtml-line-break: after-white-space; "><BR><DIV><DIV>On Apr 21, 2006, at 8:39 AM, Cornutt, David K wrote:</DIV><BR class="Apple-interchange-newline"><BLOCKQUOTE type="cite"><SPAN class="Apple-style-span" style="border-collapse: separate; -khtml-border-horizontal-spacing: 0px; -khtml-border-vertical-spacing: 0px; color: rgb(0, 0, 0); font-family: Helvetica; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; -khtml-text-decorations-in-effect: none; text-indent: 0px; -apple-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "><SPAN class="446303515-21042006"><FONT face="Arial" color="#0000ff"><SPAN class="Apple-style-span" style="color: rgb(0, 0, 255); font-family: Arial; "> > </SPAN></FONT></SPAN>Glide and slew limiter. What's the difference?<SPAN class="446303515-21042006"><FONT face="Arial" color="#0000ff"><SPAN class="Apple-style-span" style="color: rgb(0, 0, 255); font-family: Arial; "> </SPAN></FONT></SPAN><DIV><SPAN class="446303515-21042006"></SPAN> </DIV><DIV><SPAN class="446303515-21042006"><FONT face="Arial" color="#0000ff"><SPAN class="Apple-style-span" style="color: rgb(0, 0, 255); font-family: Arial; ">As I understand it, a conventional glide circuit is basically a two-pole</SPAN></FONT></SPAN></DIV><DIV><SPAN class="446303515-21042006"><FONT face="Arial" color="#0000ff"><SPAN class="Apple-style-span" style="color: rgb(0, 0, 255); font-family: Arial; ">low-pass filter, so its response is that of a discharging RC circuit:</SPAN></FONT></SPAN></DIV><DIV><SPAN class="446303515-21042006"><FONT face="Arial" color="#0000ff"><SPAN class="Apple-style-span" style="color: rgb(0, 0, 255); font-family: Arial; ">when the input changes, the output changes rapidly at first, and then</SPAN></FONT></SPAN></DIV><DIV><SPAN class="446303515-21042006"><FONT face="Arial" color="#0000ff"><SPAN class="Apple-style-span" style="color: rgb(0, 0, 255); font-family: Arial; ">more slowly as it approaches the input voltage. A proper "slew limiter",</SPAN></FONT></SPAN></DIV><DIV><SPAN class="446303515-21042006"><FONT face="Arial" color="#0000ff"><SPAN class="Apple-style-span" style="color: rgb(0, 0, 255); font-family: Arial; ">in my mind, should be linear in response: When the input changes,</SPAN></FONT></SPAN></DIV><DIV><SPAN class="446303515-21042006"><FONT face="Arial" color="#0000ff"><SPAN class="Apple-style-span" style="color: rgb(0, 0, 255); font-family: Arial; ">the output should change at an absolute maximum V/sec until it</SPAN></FONT></SPAN></DIV><DIV><SPAN class="446303515-21042006"><FONT face="Arial" color="#0000ff"><SPAN class="Apple-style-span" style="color: rgb(0, 0, 255); font-family: Arial; ">reaches the input voltage. (Of course, if you use this on a pitch CV</SPAN></FONT></SPAN></DIV><DIV><SPAN class="446303515-21042006"><FONT face="Arial" color="#0000ff"><SPAN class="Apple-style-span" style="color: rgb(0, 0, 255); font-family: Arial; ">in a V/oct system, it will give you a non-linear response with respect</SPAN></FONT></SPAN></DIV><DIV><SPAN class="446303515-21042006"><FONT face="Arial" color="#0000ff"><SPAN class="Apple-style-span" style="color: rgb(0, 0, 255); font-family: Arial; ">to pitch.)</SPAN></FONT></SPAN></DIV><DIV><SPAN class="446303515-21042006"></SPAN> </DIV></SPAN></BLOCKQUOTE></DIV><BR><DIV>I tend to agree with you that something called a "slew limiter" should probably have a linear time/voltage change response curve, but the words "glide" and 'portamento" don't necessarily connote any particular type of time/shape response. In the world of existing analog synth designs, you will find either of those words used to describe circuits that give both linear and log responses. For instance, the Minimoog, which has a decidedly linear portamento response, calls it "glide". Other Moog synths, such as the Moog Rogue and MicroMoog, which have decidedly log portamento shapes, also call it "Glide". The Prophet V and Sequential Pro One also have linear response portamento, but call it "Glide" on the front panel. The TB-303 has a log glide, and the front panel calls it "slide", probably in reference to the way a bass guitarist sometimes "slides" between notes (the Roland engineers, in their wildest dreams, never imagined that the 303 would ever be used in the way that eventually made it iconic. They were just trying to help low-budget lounge musicians replace the bass guitarist)</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV>It may be interesting to note that with the human voice and with instruments such as trombone, the violin family, slide guitar, pedal steel, and fretless bass, that do not have mechanically imposed sharply delineated pitch points, the tendency is almost always to slide between notes with an approximation of a logarithmic portamento curve -- we slide quickly toward the target note, and then gradually and more slowly settle into the final pitch as we get closer. It's subtle sometimes, but it's almost always there. indeed, it's virtually impossible to sharply and immediately jump from one accurate pitch to another when singing. Go ahead, try it -- if your ears are worth a damn, and you're honest with yourself, you'll see what I mean. Conversely, it's almost just as impossible to approximate a true linear glide with your voice (if you're trying to start and stop exactly of specific pitches). </DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV><SPAN class="Apple-style-span">The fact that pitch correction software algorithms, such as Antares Autotune, are able to eliminate this momentary human portamento (even with "singers" who, unlike Britney Spears and her ilk, actually CAN sing in tune -- for example, Shania Twain, who is a seriously good vocalist, yet for some aesthetic reason still insists on using Autotune on every track she records -- I suspect because it somehow heightens her image as the postmodern, preternaturally hyper-sexual uber-cowgirl robot queen, not unlike something one might encounter on the ubiquitous video screens of the oversexed dystopia described in Aldous Huxley's <I>Brave New World</I>) -- this unnaturally eliminated portamento gives vocals that are recorded with the software part of its characteristic sound, especially if you turn the software's "speed" control to its fastest setting (yes, there are other factors, too). It enables humans to do the impossible: make their vocal tracts act like frets on a guitar.</SPAN></DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV>Robin Whittle (he of Devilfish 303 fame) once speculated that part of the 303's natural appeal to humans is because the sound of the glide was very reminiscent of the sound of a baby animal's cry. I would probably agree with him, but I would simplify that to say that we are simply naturally attuned to the sound of a non-linear, logarithmic pitch change. It's just how nature sounds Linear glide isn't, nor are linear-shaped envelopes, for that matter.</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV>BTW -- Keith Emerson's iconic solo at the end of "Lucky Man"? Log glide. In my opinion, that solo would have sucked with linear Minimoog-type glide.</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV>Mike B.</DIV><DIV><BR class="khtml-block-placeholder"></DIV></BODY></HTML>