rAudio 1 • 20210708: Add - Permanent VU meter mode

[klassikmann]

First observations after enabling permanent VU meter:

• Stuttering sound during first one or two seconds (performance constraint?),
• VU meter increases to 80% until 100% very soon and remains in this range most of the time.

Kernel: 5.10.46-1-ARCH aarch64
Hardware: Raspberry Pi 3 Model B Rev 1.2