Question: I don't have perfect pitch and badly trained and imprecise relative pitch. I only started two years ago to learn musical notation as a hobby and writing little stuff for myself and friends ([For example](https://www.youtube.com/user/franklinvp?feature=mhee)). I said this just to give a context that I am not a musician and that I certainly ignore many basic things about notation, terminology, and the capabilities of the different musical instruments.
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The question.

I imagine there are ways to get a recorded natural occurring sound and somehow make the sound into a MIDI file, for example, and then open the MIDI, let's say in Sibelius and that should give an approximation for how its transcription into the score should look like. 

Some composers manage to write down parts for an instrument that makes it resemble a particular natural occurring sound (horse whinnying, bird songs, rain, ...). My aim is to have a technical procedure to help myself in the process of doing that. Something that gives me a first approximation of notes that I can afterwards, by hand, tweak to make it more like the natural sound I wanted, or make it more playable, and then be able to elaborate them into a larger composition.

Does anyone know ways in which this can be done? Suggestions?

Answer: 
I think that you probably mean ["whinnying" of a horse.](http://www.youtube.com/watch?v=yCkSJhCD6SA)

With brass instruments, it's typically done with a valved instrument, such as a trumpet or a tuba (or valve trombone if you have one.) The sound is typically produced by pressing the valves halfway down and either shaking the instrument (in the case of a trumpet) or by making a very wide vibrato. Using a tuba is less effective as it tends to sound more like a whale.

On trombone, especially without a valve, the effect may be harder to reproduce. A possible solution may be to have them use a straight mute.

Alternatively, the effect could be created by a percussionist making the sound through a megaphone - they love stuff like that.

Or as another idea, you could have a recording of a horse whinnying and then cue the recording in the score.

As far as notation goes, the easiest thing would probably be to just put a note in the score that says "whinny like horse" with perhaps an "x" for a note head; as long as the duration of the sound is clear. In addition to that, you may want to put a note at the front of the score explaining how to produce the sound as well as putting that same note at the bottom of the part for the instrument you write it for.

As for other naturally occurring sounds, you'll want to become more familiar with percussion instruments. For example, a "sea drum" simulates the sound of rolling waves, a "wind machine" generates the sound of wind, an aluminum sheet can mimic thunder, a clipboard can mimic a whip, temple blocks can mimic horse hooves, etc etc.

For bird sounds, you can check out the "Spring" movement of Vivaldi's *Four Seasons* where he mimics the songs of birds in spring. Also check out work by Olivier Messiaen, who was infatuated with birds and transcribed many of their calls, and even wrote works using his transcriptions.

Hope that helps.
You may find that, unfortunately, the best technology can do at this point is going to be somewhat below your expectations. Transcription is something even humans struggle with, and the more complicated a piece of music (audio) is, the trickier it is to transcribe--either for human OR computer, but the limit of a computer program is going to be far below that of a capable human. The more polyphonic, the trickier it is to transcribe.

[AudioScore](http://www.neuratron.com/audioscore.htm) is probably the most widely-known tool that does what you are talking about, since a lite version is bundled with Sibelius, but those tools are almost never perfect, and output typically requires a lot of tweaking from the user.

If you're looking at birdsong in particular, though, that's essentially monophonic (single-line) music with no easily quantifiable rhythm. So, I wouldn't put too much faith in the software's ability to notate the rhythm, but it may be fairly successful with the pitches--and even if it's not totally accurate, good transcription software will be able to show you a spectrogram that visually places pitch occurrences over time on an axis (see the first screenshot on the AudioScore link above).