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Technical information on computer specs for Hauptwerk
Part 1: polyphony
When you engage several stops on an organ and play a chord, a lot of pipes sound simultaneously. For example, suppose you have 10 stops drawn and you play a 10-note chord (5 keys with each hand). Usually 10 x 10 = 100 pipes will be sounding simultaneously. Since Hauptwerk uses one sample per pipe, playing and holding such a chord in Hauptwerk means that Hauptwerk must play 100 samples simultaneously, and thus consume 100 voices of polyphony.
Since Hauptwerk uses release samples to reproduce the natural decay of the pipes and, optionally, also the acoustic (reverberation) of the room, those samples must continue to play after you release the keys. If the reverberation tails are long, perhaps 2 seconds, then that chord will continue to consume 100 voices of polyphony for an extra 2 seconds after you release the keys. So if you play a fast piece of music, the polyphony demands may be very high. For example, suppose you play chords of 4 notes with 10 stops drawn, at a rate of 5 chords per second, and the average length of the release samples is 2 seconds. You then need a polyphony of 4 x 10 x 5 x 2 = 400 voices.
However, if the samples are 'dry', with no reverberation recorded into the release samples then the release samples will be much shorter - perhaps 0.5 seconds, and you would need a polyphony of only 4 x 10 x 5 x 0.5 = 100 voices to play the same piece. So dry samples require much less polyphony than 'wet' samples. However, wet samples capture the natural acoustic of the room, which is often much more realistic for listening at home, especially with historic organs where the acoustic is an integral part of the sound.
Hauptwerk has an advanced polyphony management system, which allows you to specify the maximum polyphony that your computer hardware can achieve after testing it initially. When Hauptwerk reaches that limit, no more pipes are allowed to sound, preventing the system becoming overloaded and the audio breaking up (very important for live recitals!). A little before the limit is reached, Hauptwerk attempts to fade out some of the most inconspicuous release samples, so that even reaching the polyphony limit is extremely rare. In practice this means that you can choose your computer hardware to support the polyphony that you will need for average playing, and let Hauptwerk's polyphony management system handle extreme loads safely, usually with no audible loss of quality.
The limit can be fine-tuned separately for each sample set, and processor-intensive features can be enabled or disabled separately for each sample set, so that you can get the best balance of performance and realism that your computer hardware can handle for the sample set.
If, for example, you expect to play a sample set with 2 second reverberation, and anticipate that you would normally not use more than about 10 stops with 3-note chords in each hand (6 keys), at a rate of 3 chords per second, then, as above, you would need a true polyphony of 6 x 10 x 3 x 2 = 360. As a rule of thumb, we would recommending choosing your computer hardware to be able to handle 3 times that polyphony, which would give optimal performance for the vast majority of the time, whilst Hauptwerk's polyphony management system will handle extreme loads unobtrusively and safely. Hence, with this example, you should choose a computer that you would expect to be able to handle about 1000 simultaneous pipes (all of our recommended computer system would be adequate with all Hauptwerk realism features enabled).
As a very, very rough guide, we would recommend that for average use you might choose the overall maximum polyphony required as follows:
- 500+ voices of polyphony for medium-sized organs (30 ranks or less) with dry samples.
- 1000+ voices of polyphony for large organs (30-60 ranks) with dry samples.
- 800+ voices of polyphony for medium-sized organs (30 ranks or less) with wet samples.
- 1700+ voices of polyphony for large organs (30-50 ranks) with wet samples.
- 2400+ voices of polyphony for extremely large organs (50 or more ranks) with very long reverberation (the largest cathedral organs).
The polyphony is the main factor that determines the processing power you need. In summary it depends on:
- How 'wet' the most reverberant sample set you plan to use will be (average decay time).
- The maximum number of stops you will engage at once (more stops tend to be drawn simultaneously on larger organs).
- The type of music you will play - speed and number of simultaneous notes.
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