A regenerative controller is one which over-compensates, either by design or accidentally. Richard describes a regenerative suction regulator which evidently increases the suction in the action stack as more notes are played. This behavior is in stark contrast with the Duo-Art stack regulator which supplies less suction as more notes are struck together in a chord. -- Robbie
From: firstname.lastname@example.org (Richard Stibbons) To: email@example.com Date: Mon, 8 Jan 2001 17:06:38 -0000 Subject: Regenerative Suction Regulator Dear MMD, I once owned a coin operated Hupfeld cafe piano which had an intriguing label on the pump. It read: "The pump must make 70 revolutions per minute. More revolutions will cause disturbing noises and less revolutions will impair the expressions" The latter comment was interesting because the piano was no more than an electrically pumped 88-note player with a simple stack regulator and a pair of theme valves. The reference to "the expressions", therefore seemed a little optimistic. When it was given to me in 1960, the instrument was untouched internally, the motor having burned out in the early 1930s. All it needed was a new motor and for the heavy hoses to be replaced, whereupon it sprang to life, playing well and, to my astonishment, producing quite considerable expression. Doubting my ears, I put a gauge on and the vacuum was indeed varying between about 8 and 24 inches water column. This turned out to be due to deliberate over-compensation in the stack regulator, achieved by using a weak spring. The effect is familiar with wind motor governors which, if the spring is too weak, actually slow down as you pump harder. Applied to the stack regulator the effect causes the piano to play louder as the demand increases. Therefore, crashing chords really do crash and single notes play softly. This is entirely appropriate for the "Bier Keller" style of music this piano was designed to play. I still have a roll which came with it which I recently scanned and then wrote a simple expression program to emulate the effect. (Hupfeld.mid attached). To most ears, 1920s German pop was not great music but the result is interesting, especially when viewed in Cakewalk or a similar program which shows the note velocities. It was obviously arranged with the deliberate intention of creating 'the expressions'. There is no soft pedal, all the expression comes from the 'velocity versus demand' effect described, enhanced only by the theme perforations. The technique is very clever by virtue of its simplicity, characteristically Teutonic, but it could easily be missed in restoration. I've always wondered if it is widely known about and used in other instruments ? Richard Stibbons Cromer, England -------------------- From: firstname.lastname@example.org (Richard Stibbons) To: email@example.com Date: Tue, 9 Jan 2001 09:49:07 -0000 Subject: Hupfeld Animatic Clavitist Rolls Hi Robbie, The piano in question came into this country in the early 1920s. Unfortunately, this was a time when all things German were somewhat unwelcome here. As a result, Keith Prowse who marketed it, went to some lengths to conceal it's country of origin. It was badged "Keith Prowse, London" and it was only the "LH" logo cast into the frame which revealed it's true identity to the initiated. The piano was an Animatic Clavitist identical to that shown lower left on page 434 of the Bowers' Encyclopedia, "Animatic Clavitist with orchestra cabinet." It was capable of driving a bandbox, having a multi port connector block near the wind motor, but this optional extra had never been purchased. There was a switch in the spool box which turned the band box on and off. It would probably have had about 12 small pipes and bass and snare drums. I have two rolls which belonged to it, both with three tunes. They are very high quality and clearly German made. The MIDI file I sent you doesn't have the band tracks although it does have a mandolin track. It has no markings of any kind at either end. The other roll carries a Keith Prowse typewritten label. The label is now illegible but the middle tune is "Red Red Robin". The rolls are very interesting because they use both square and round perforations. They were either made on a very sophisticated perforator or were the result of a 'double pass' process. I presume this technique was another way of achieving a degree of expression. I don't know how much is known of this process. I can make a pictorial scan of a section if you're interested. The second roll has band box perforation tracks but, as far as I can tell, no expression although there is a soft pedal track. I can scan it for you if you wish but I haven't written a program for reproducing the band parts and it's hardly worth doing so for just one roll. I sent you the simple roll because it was a less confusing demonstration of the point I was making. As I said, I have long wondered if this clever technique for generating expression is known about amongst the modern fraternity. There are three tunes on the roll I sent. The first one is damaged but the tune is "I Wonder where my Baby is Tonight". Like you, I recognized "Always" but not the third tune. This was an extremely rugged and well-made instrument, and one of the best things about it was that it lived from new in the front parlor of a child-free private house. There's a poignant story behind the fact that by 1960, it was still "as new". It was unmarked and untouched inside and out and still had the original beaded lampshades. Even the open mercury dashpot switches were filled and working! Like much of my collection, it had to go when I moved house and I passed it on to a small museum in Southern England. Best wishes Richard Stibbons -------------------- From: firstname.lastname@example.org (Richard Stibbons) To: email@example.com Date: Thu, 11 Jan 2001 10:25:05 -0000 Subject: Regenerative Suction Regulator The interesting correspondence from Tom Jansen [010112 MMD] tends to confirm my theory that modern experts have lost sight of this clever yet simple technique. It is, after all, merely a matter of adjustment of the regulator spring and few restorers or technicians would leave it unusually weak unless they were aware of this idea. I trust you will agree this effect is not a figment of my imagination. I was quite surprised at the expression which appeared when I wrote this experimental software. The program is very primitive yet, musically, the results are a big improvement. I am in no doubt that Hupfeld used this technique in a deliberate and controlled manner but have always wondered if other manufacturers around the world also knew of it. I have processed scans of some of the more boisterous QRS rolls using the same algorithm and they certainly produce expression which is, in most cases, an improvement on the "constant volume" sound. Is it possible that US manufacturers might have used the same trick ? The discussion about the Animatic Clavitist is another issue. I was never certain what was inside the "orchestra" box and a xylophone does make sense. The scale is well documented and I attach a scan of what is probably an "S" roll. My piano had the ingenious mandolin system mentioned and also used pneumatic logic gates characteristic of Hupfeld. For example, the "motor off" track cut the motor but, when opened in combination with the "soft pedal" a special latch operated which initiated reroll. One aspect which neither of your experts mentions is the use of square and round punches on the same roll. This would have been a major manufacturing complication and there must have been a good reason for doing it but I wonder what it was ? I attach a pictorial scan of a small section. These rolls are fully of mysteries. The use of the themes is surprising in the musical sense. In addition, many of the "snakebites" are out of position. Having examined the rolls more closely, I'm beginning to revise my opinions about the quality. Physically they are superb but there are several bouts of "lumpiness" in the tempo and this, together with the misplaced themes, makes me suspect that these rolls are copies which might be several generations old. I attach (1) a pictorial scan of part of one of the rolls; (2) a MIDI file of one tune; all tracks are intact, only the webbing has been removed; (3) a MIDI file as above but processed with my algorithm which increases volume in accordance with an estimation of the vacuum demand at any instant. The control tracks have been removed. Best wishes Richard Stibbons
stibbons_Hupfeld.mid (39 kb) -- transcription of music roll note channels, processed with algorithm which increases volume in accordance with an estimation of the vacuum demand at any instant.
stibbons_AnimaticSunproc.mid (25 kb) -- transcription of music roll, including control tracks
stibbons_AnimaticSproc.mid (21 kb) -- transcription of music roll note channels, processed with algorithm which increases volume in accordance with an estimation of the vacuum demand at any instant.
stibbons_AnimaticS.jpg (328 kb) -- image of music roll presumed to be Animatic -S-
stibbons_AnimaticS.gif (24 kb) -- image file converted to GIF