Emulators and Translators
By Robbie Rhodes
In digest 960307 Wayne Stahnke wrote:
> To hear the performance, you need a program that models the
> behavior of Ampico instruments.
We have applied the term "Emulator" to any hardware and/or software process which duplicates the essential (as in "essence") function of another "real" process. The internal functioning of the emulator is immaterial -- the only requirements is that the output data from the emulator is the same as the output data from the "real" process which is emulated.
An emulator for a reproducing piano roll receives as input the same binary data that exists at the tracker bar and valves of a pneumatic piano. The output data from the emulator is sound: acoustic sound pressure, generated by an electronic synthesizer, amplified, and converted to acoustic pressure by a loudspeaker.
In evaluating the faithfulness of the processes which Wayne Stahnke and I are discussing it is appropriate to ask, "What is the Measure of Success?"
The very practical, and obvious, Measure of Success in preserving music roll binary data is to punch a roll from the recovered Master Roll file, lay it against an original, and inspect it!
The measure of success of the reproducing piano emulator is in the listening. Horst Mohr built a _complete_ Ampico-A emulator. The input is an Ampico roll, the output is music from a loudspeaker. Within Horst's emulator system is a software element which converts Ampico binary data into MIDI data. If Horst has a _really good_ piano synth (which converts MIDI data into electric signals), a listener should be unable to discern the difference between his emulator system and a real Ampico piano.
For simplicity we will call the "Ampico to MIDI" process the "Ampico Emulator", while bearing in mind that this is simply one of the elements of the overall Ampico-to-sound emulator system.
Emulators for "Ampico to MIDI", "Duo-Art to MIDI" and "Welte to MIDI" have been written by Richard Brandle and Wayne Stahnke. I wrote a "Ampico-B to MIDI" emulator first, because that is the simplest, and I am developing my "Ampico-A to MIDI" emulator. The latter seems to yield musically pleasant results, but I haven't yet held "comparison listening tests" to determine its Measure of Success! I will prepare a MIDI file of the Rachmaninoff roll and post it to Jody's ftp account for all to evaluate. But be patient; it will be several weeks.
How does one create an Ampico roll from an original DuoArt or Welte performance? Answer: by using a translation process. We use this term because of the analogy to translating text from one language to another. The content is the same in both languages, the difference is in the vocabulary and grammar rules. Most important, the data is already edited for a split-stack piano.
Translation of music roll data between different reproducing piano formats is much, much simpler than converting a MIDI performance recording to play on a pneumatic reproducing piano. This is because a MIDI output device, like a synthesizer or solenoid piano, can play notes simultaneously with differing velocities, whereas the pneumatic reproducing piano (and its electric relative, the Marantz PianoCorder), must strike simultaneous notes at the same velocity. Converting MIDI files to rolls for these "split-stack" machines requires the same tedious manual editing that was needed in the 1920's. I believe that a computer process can only aid, but not supplant, the work of a skilled, musically-trained editor.
The executives at Ampico in 1927 probably asked Mr. Stoddard and Dr. Hickman if an automatic machine could be built to create music rolls directly from the data recorded by the spark chronograph recorded. I wonder what the reply might have been...!
Translator boxes were built in past years by Wayne Stahnke and Will Dahlgren which perform simple real-time conversion between serial data formats for devices such as PianoCorder and IMI Cassette Converter. For the most part the users of these simple boxes are satisfied if the music is pleasant-sounding; knowledgeable listeners ("piano critics") claim that the translation is deficient. The simple boxes do have a notable feature: they seem immune from claims of Copyright Infringement, because a permanent data record (a disk file) is not created!
-- Robbie Rhodes
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(Message sent Sun 10 Mar 1996, 06:49:40 GMT, from time zone GMT-0800.) |
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