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Comment by dmlorenzetti | Hacker News Reader

I once went with a friend to price electric pianos. The models she was looking at sampled traditional pianos to get their notes, and had a switch to toggle between different sampled instruments.

She asked why there was such a price difference between models, based on the number of keys (unfortunately I don't remember the numbers anymore, but basically some of the models had shorter keyboards).

The response was that, for models with a smaller number of keys, they could just sample one octave of the original instrument, and scale the frequencies electronically. However, once you go beyond a certain range, straight scaling didn't work anymore, so they had to sample the whole range of a traditional piano-- hence more electronics needed in the electric piano.

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I don't buy it. Sampling isn't typically done for an entire octave and then scaled 2× or ½×; that would sound terrible. Rather, usually every 3rd note (or so) is sampled, and the "missing" notes are scaled from those.

More likely the reason is that keyboard size is used as a proxy to discriminate between amateurs (who can play most anything they care to on, say, a 61-key keyboard) and professionals (who would look like fools trying to fit certain pieces into 61 keys when they are meant for the full 88).

You might be surprised at the results you can get these days. There are even "soft pianos" that are almost completely synthesized rather than sampled. They can sound amazing: http://www.truepianos.com/demos.php

Analog modelling ("the soft pianos" you mention) don't have much to do with stretching samples for several octaves the OP described.

I don't think any of the models sampled one full octave and then resampled that for the other octaves. When you change the pitch of a recorded piano note through resampling, it's going to sound very artificial if you go beyond a couple of semitones. Typically you spread the samples out so you have 3, 4 or 6 per octave.

Also, most electric pianos support transposing the whole keyboard, which means that even when you just have four or five physical octaves, you can play notes lower than or higher than that. So that explanation for the price difference is not very realistic.

Typically keyboard instruments come in '60 key' (aka 5 octave) as budget models, and 88 key (7+ octaves, piano equivalent) 'pro' models. Budget samplers sometimes sample a single octave and use integral sampling changes to fill in the rest of the octaves. That used to be to save memory (which was expensive) although it is less of an issue now.

That said, it had nothing to do with being even tempered or not, it had to do with cost. But as Yamaha and others also point out, the harmonics on every key of a piano are slightly different because the keyboard is constructed with all those hammers and strings, one for each key.

>The response was that, for models with a smaller number of keys, they could just sample one octave of the original instrument, and scale the frequencies electronically.

That's not the case. It's trivially easy and cheap to sample the full scale or close to it. No manufacturer I know uses just one octave (or even just 2 or 3). And beyond 1 octave of stretching this would sound attrocious anyway.

Probably a misinformed salesman. Back in the day (eighties, early nineties) people would do something like that, but mostly for digital samples of things like a bass, flute, etc, to conserve space in the, then, limited storage of samplers.

The price difference in digital pianos has to do with brand name, mechanical and build quality (e.g key mechanism, speakers, D/A converters etc), and extra capabilities (sequencer, etc).

The NRE and storage for additional samples isn't that much cost - now. 20 years ago, yeah. Cost is way dominated by the number of parts in the MIDI controller used.

Piano sample sets can now run into the gigs of memory - a now-defunct product that pioneered this was actually called Gigasampler.

For a file format that describes how samples relate to MIDI notes, google for "SFZ files".

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