The minValue read-only property of the AudioParam interface represents the minimum possible value for the parameter's nominal (effective) range.
A floating-point Number indicating the minimum value permitted for the parameter's nominal range.
The default value of minValue is the minimum negative single-precision floating-point value (-340,282,346,638,528,859,811,704,183,484,516,925,440).
const audioCtx = new AudioContext();
const gainNode = audioCtx.createGain();
console.log(gainNode.gain.minValue); // -3.4028234663852886e38