It depends on the format.
Decompress On Load - Audio files are decompressed as soon as they’re loaded. Use this option for smaller compressed sounds to avoid the performance overhead of decompressing on the fly. Be aware that decompressing Vorbis-encoded sounds on load will use about ten times more memory than keeping them compressed (for ADPCM encoding it’s about 3.5 times), so don’t use this option for large files.
Godot does not do this. Instead, Godot supports WAV files which are uncompressed and recommends you use them in this context for sound effects.
Compressed In Memory - Keep audio compressed in memory and decompress while playing. This option has a slight performance overhead, especially for Ogg/Vorbis compressed files. Use it only for files that consume excess memory for the Decompressed on Load. The decompression happens on the mixer thread, which can be monitored in the DSP CPU section in the Audio pane of the Profiler window.
If you use an MP3 or Ogg/Vorbis file, this is how Godot loads it.
Streaming - Decode continuous audio. This method uses a minimal amount of memory to buffer compressed data that’s incrementally read from the disk and decoded spontaneously. The decompression happens on a separate streaming thread whose CPU usage can be monitored in the Streaming CPU section in the Audio pane of the profiler window. Note: Streaming clips have an overhead of approximately 200KB, even if none of the audio data is loaded.
AFAIK, Godot does not support streaming audio.
More details with your issue might help us find you another solution. If the file is large and you want to load it before it gets called, you can just use preload().
# Load it as a const
const BIG_SOUND_FILE = preload("res://my_big_sound_file.mp3")
# Or load it as an onready variable that loads when the scene loads
@onready var big_sound_file: AudioStream = preload("res://my_big_sound_file.mp3")