Absolute Volume

USB DACs and Bluetooth DACs receive digital audio signals from a source device and perform Digital-to-Analog (D/A) conversion.

When adjusting the playback volume on a PC or smartphone (the source device), the most common method is to reduce the source device’s output volume before transmitting the digital audio signal to the USB DAC or Bluetooth DAC.

Examples of volume control methods include:

• Volume slider in audio or media players

• Volume slider on streaming platforms such as YouTube

• Playback volume control in applications such as Foobar2000

In these methods, the digital audio signal retains full bit resolution only when the volume is set to maximum. Reducing the volume lowers the digital signal’s amplitude, resulting in a loss of bit resolution and potential degradation in audio quality.

When adjusting the volume through these methods, the audio signal is scaled down, which can reduce sound quality.

The Absolute Volume adjustment method avoids this issue. With Absolute Volume, the source device always transmits the digital audio signal at its original, full-scale amplitude. The volume control information (volume level) is transmitted separately to the USB DAC or Bluetooth DAC, which adjusts its output level internally based on the received command.

All major operating systems — Windows, macOS, iOS, and Android — support the Absolute Volume method.

However, there is a known issue in Android OS where the USB Audio Class implementation does not support the Absolute Volume feature. As a result, when an Android smartphone is connected to a USB DAC, Absolute Volume is not applied, and volume control is performed by scaling the digital audio signal on the source device.