How to use the practice materials
Once you have registered for a place in the concerto competition, you will be sent the relevant links to all the performance and practice materials.
The performance materials comprise:
A video with music notation of the complete performance (piano with orchestra)
The same video of the orchestra part only (this will be the version used in the public performance)
The practice materials comprise:
Several shortened versions of the orchestra only video between rehearsal marks (to make it easier to practise smaller sections) and audio files.

1/ Start by listening to the complete version - several times. Do this, as much as you can, by listening only and without following the music notation of the piano part.
Get used to what the orchestra sounds like and where you come in after the introduction.
2/ Next, listen to the orchestra only version and play along in your head (not yet on the piano). Do this several times as you familiarise yourself with what is happening in the orchestral part.
3/ Start practising your part with the orchestra. Make sure you have the speaker volume turned up high enough and play quietly to begin with in order to hear that you are playing on time with the orchestra.
4/ Use the practice materials to help you practise smaller sections

Tips!
Rely on your ears! You should practise by listening to what you are playing and how this fits with the orchestra. This may be a new experience for you, but stick with it and you will learn a better way to play the piano!
The orchestral part has constant rhythmic cues. Learn where these are and, if it helps, write the cues into your piano part.
Do not practise using headphones, as this will not allow you to hear your own part sufficiently. You can use ear buds, but be careful not to have the volume turned up too high.
Find somewhere that you can practise playing your part whilst the orchestral part plays through external speakers. You can buy your own bluetooth external speaker such as the Sony SRS XB100, here, or the Ultimate Wonderboom 4 bluetooth speaker, here. They are not expensive but they are good quality, and this is what you need to fully appreciate the orchestarl instrument and best hear what is going on.
Of course there are many other brands, and you can do your own research, but there plenty of sites which offer reviews and good advices such as this one.
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