What is a Virtual Orchestra?
When I was a young man studying orchestration and music theory, the only way to hear your compositions was to have them played by living, Mark 1 human beings, AKA an Orchestra. We had synthesizers with "string" and "brass" sounds, but they sounded, well "synthy". They were nothing like a real orchestra.
In the 1980's sampler technology started to become available. The samples at first were mostly short and limited in variety. The best sample libraries of the time cost thousands of dollars. Most of these libraries required expensive hardware on which to run them. In the late 1990's and early 2000's, computer power began to reach a point where it was beginning to be possible to have the computer act as a sampler. This opened up the possibility for Virtual Instruments whose sound was generated by audio samples. Computer power is now at a point where the sample libraries of 20 years ago that cost thousands of dollars are the entry level libraries of today. One library, Miroslav Philharmonik originally sold for over $4000.00. You can now purchase this library for about $120.00!
A sampler is a hardware or software instrument that makes sound by playing back
short recordings or "samples" of real-world sounds. For example, a recording can be
made of a violinist playing an A. When the A key is pressed on a keyboard connected
to the sampler, the sample of the violinist playing the A will sound.
A composer can now compose and record his or her music with a computer and have it played back using high quality samples that rival real-world, live performances. For an excellent example of just how realistic sampled music can be, see this video of the Planets Suite on YouTube: https://www.youtube.com/watch?v=9OsGjbl0vbY . The video is a real orchestra but the sound is entirely made up of sampled sounds that is, a Virtual Orchestra!
A Virtual Orchestra is created when a composer writes or plays a composition into a computer program called a DAW (Digital Audio Workstation). The music is than played back by assigning virtual instruments to each track. For example, if the 1st violins need to play in the legato style, the composer will assign a sampled violin section playing in the legato style. The DAW can then play the composition back using the sampled sounds. To be clear, I am grossly understating the amount of work required. Even with the fantastic sample libraries available today, there is a large amount of very careful "programming" that has to be done to get the tracks to sound like a live orchestra. Or at least sound close to a live orchestra.
What turns me on about the digital age, what excited me personally, is that you have
closed the gap between dreaming and doing. You see, it used to be that if you wanted
to make a record of a song, you needed a studio and a producer.
Now, you need a laptop.
About Sample Libraries
Usually there are thousands of samples recorded in an orchestral sample library. For example, the 1st violins would have every note in their normal range recorded sustained, with tremolo, pizzicato, marcato, staccato, staccissimo, muted, sul ponte, Bartok pizzicato, legato, portamento, slurs, etc. This is then repeated for every section of the orchestra. That's a lot of samples! I have well over 1 terabyte (TB) of samples in my sample library.
To sum up, a Virtual Orchestra is a toolset a composer uses to have his or her compositions "played" by real musicians. If done well, a mock up created with orchestral samples can sound very close to the real thing