A4 — Sets the base frequency for pitch A4.
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.
A4 = (optional) -- set reference frequency for pitch A4 to iarg Hertz. The default value is 440.
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 6.08, A4 may be used. It affects the behaviour of the opcodes cpspch, cpsoct, cps2pch, cpsxpch and cpsmidinn.