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This may be somewhat subjective, though it may be verified by a breakdown of the audio. But it seems easy to find like drums and other percussion, bass guitar, piano, harpsichord, maybe harps and organs, and others that sound realistic. But then like many horns or string instruments don't sound realistic. What is the reason for this?

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    Note that all the ones you note as being less realistic have a component of expression after the note is started (breath, bow...)
    – Tom
    Aug 12, 2023 at 17:30
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    Jaron Lanier writes in his excellent You Are Not a Gadget about knowing the guy who invented MIDI to get his keyboard synths to talk to each other. Keyboards are based on a particular on/off time with a given velocity, and so MIDI models this well, but it's bad at more expressive instruments (e.g. a violin sliding through pitches in a single stroke -- often replicated as multiple notes with suppressed attacks). But due to technology lock-in, MIDI became the standard for every instrument. This is the reason for the superiority of percussive virtual instruments as the answers below note. Aug 13, 2023 at 5:17
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    Are you saying there may be better options than MIDI?
    – user94172
    Aug 13, 2023 at 5:20
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    Add to your list of the difficult to sample the singing voice, with all the nuance of voice type, timbre, vowels, consonants---good luck!
    – nuggethead
    Aug 13, 2023 at 11:36
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    "I'm more talking about for putting together music ... in a DAW" - the better option than MIDI is microphones, record players, and you sampling actual instruments. I can tell from down the block that it's fake drums, and that's the 'easy' one to do.
    – Mazura
    Aug 13, 2023 at 18:06

3 Answers 3

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Compressing 30 years of research into a couple of short paragraphs…

Non-percussive instruments are what's known in the trade as "an absolute b**ch to sample" because they can change over time, unlike a percussive instrument which has a relatively simple release phase after the initial impulse.

Some huge sample libraries use many many variations of each possible note & how it might be played. The user has to choose individual 'articulations' to persuade the ear that this is a natural progression. This is often combined with a 'round robin' structure which will play a different sample of each note each time it's re-triggered, to prevent the 'machine gun' effect of every one being exactly the same.

The player can help this along by modulating volume/vibrato etc over time, though the sound will not change to fully express the actual sound of a violinist playing harder or adding ever-changing vibrato.

There's a niche manufacturer who took an entirely different approach. Rather than each note being one of a selection of pre-recorded samples, each instrument is built from tiny snippets of sound, which can morph one into the other whilst the note is playing. This then sits within a mathematical model of the physics of the instrument string/wind/body.
Here's a demo - AudioModeling, SWAM

One thing to note - the harder it is to make each of these, the more expensive it is ;)

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  • That alternate approach sounds interesting, I guess it could automatically add some unique randomness to each note played.
    – user94172
    Aug 12, 2023 at 17:52
  • It's always random, because it's calculated millisecond by millisecond. It'e never the same twice. You should be able to play the same part twice on two separate tracks & not hear them phasing.
    – Tetsujin
    Aug 12, 2023 at 17:56
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    Physical modelling has always been computationally expensive. I worked alongside the team that built the first ever physical modelling synth, in the early 90s. At the time, the sound design was done on the fastest computer generally available, the Sun Sparc. Every time a parameter was changed, it would take between 10 minutes & an hour to calculate the new sound. Computers have got a bit faster since - though they do still have to cut some corners to make the end result truly realtime.
    – Tetsujin
    Aug 12, 2023 at 18:06
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    To sound like any amp you could ever own, & by some clever hybridising, some that never existed. I've always been a fan, from the early days right to now. I still have a 20-year-old Variax & Line 6 'amp'. Between them the world's my oyster… or frankly, mollusc of my choice ;) The models made today are very very clever, but tbh, they reached the level of 'almost no-one can tell it's not real' 20 years ago.
    – Tetsujin
    Aug 12, 2023 at 18:49
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    The world is your oyster originally Shakespeare, later expanded by the late, great Terry Pratchett to include any mollusc.
    – Tetsujin
    Aug 13, 2023 at 9:21
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Any instrument that is percussive (you play the note and then there's almost nothing more you can do with it except stop it) is fairly easy to synthesize.

Any instrument where the player forms the note during the whole time it's played (and maybe connects it to the next note) are much harder to recreate. It's possible to make notes more expressive by modulating various parameters of the sound (volume, pitch, timbre etc.) but it takes a lot more work.

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  • And I hesitated to make my comment an answer, would never have fast enough!
    – Tom
    Aug 12, 2023 at 17:36
  • I feel like there are some exceptions, but I feel like this answer is good for the fairly general question I asked.
    – user94172
    Aug 12, 2023 at 17:38
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    Percussive instruments can be still hard to model, if you want to reproduce a large variety of articulations. But of course I agree, it adds another level of complexity, if the sound parameters change while the note is being sustained. Aug 13, 2023 at 0:25
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Others have mentioned more general answers, I'll try to provide a comparison of two real instruments.

You mentioned it was easier to find guitar samples, then it was to find stringed instruments (e.g. cello).

If we look at a solid body electric guitar, it's plucked and then the strings movement is measured by electrical signal through the pickups: enter image description here

Although other parts of the guitar might also be vibrating, most the main part of the sound is coming from the pickups.

Therefore if wanted to build a guitar synth, we would have to model how the strings vibrates and just use that signal to create our audio.

Now instead if we have a bowed cello (which looks like this, and doesn't use a pickup)

enter image description here

we can see that sound is produced by the bow moving across the string (which is more complex than just plucking the string), which then vibrates a certain string, which then vibrates the entire body of the cello producing a rich tone which doesn't take any amplification to hear.

The rich tone also arises from chladni figures, which describe the way a thin plane vibrates at different frequencies so when you play a note, the front and back of the cello may vibrate in different ways:

enter image description here

(the white and black says how much each section vibrates)

So we can see that if we put the same effort into building a guitar synth as into a cello synth, we'll probably end up with a better sounding guitar synth as we'd need more effort to model the complexity arising from the cello.

So on average this is part of why string synths may not sound as realistic as guitar synths.

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  • Cool, useful pics
    – user94172
    Aug 13, 2023 at 17:26
  • Do people use a lot of synthesized electric guitar? Amp simulations are used a lot, but it seems that guitar is one of instruments that are most often recorded with a real instrument.
    – ojs
    Aug 13, 2023 at 18:34
  • Bass guitar tends to sound nicer. Most guitars I've tried didn't sound great, but at least one company does make alright sounding guitars imho. In the demos online guitars often sound ok, but once you use them, making individual notes or chords, the quality differences become much more apparent. Single notes usually sound better than chords.
    – user94172
    Aug 13, 2023 at 20:15
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    "You mentioned it was easier to find guitar samples, then it was to find stringed instruments" This is a very, very small nitpick, but technically, guitars are stringed instruments (so are pianos too, but...). But I know exactly what you mean by that and why you said it that way. So I'm probably making a big deal over nothing.
    – Chipster
    Aug 13, 2023 at 21:12
  • I did say bass guitar. Normal guitar is hit or miss. But then like violin, I don't think I've heard a realistic one. Note chords on bass guitar aren't as common.
    – user94172
    Aug 13, 2023 at 22:02

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