These statements are global value assignments, made at the beginning of an orchestra, before any instrument block is defined. Their function is to set certain reserved symbol variables that are required for performance. Once set, these reserved symbols can be used in expressions anywhere in the orchestra.
sr = (optional) -- set sampling rate to iarg samples per second per channel. The default value is 44100.
In addition, any global variable can be initialized by an init-time assignment anywhere before the first instr statement. All of the above assignments are run as instrument 0 (i-pass only) at the start of real performance.
Beginning with Csound version 3.46, sr may be omitted. Csound will attempt to calculate the omitted value from the specified values, but it should evaluate to an integer.