Signal processing device and signal processing method

A signal processing method comprising:

• amplifying, by a first amplifier, a level of an analog audio signal input from an external source with a first gain whose value is variable;
• converting, by a converter, the analog audio signal amplified by the first amplifier into a digital audio signal;
• performing, by a signal processor, signal processing for controlling tone of the digital audio signal, the signal processing including attenuating a low-frequency region of the digital audio signal;
• detecting, by a controller, a level of the digital audio signal before the signal processing and controlling, by the controller, the value of the first gain in accordance with the detected level of the digital audio signal before the signal processing;
• and
• detecting, by a second amplifier, a level of the digital audio signal after the signal processing;
• determining, by the second amplifier, a second gain in accordance with the detected level of the digital audio signal after the signal processing and the first gain;
• and
• amplifying, by the second amplifier, the digital audio signal after the signal processing with the second gain,
• wherein the first gain applied to the first amplifier is set to be small if the level of the digital audio signal in the low-frequency region is large and the second gain determined by the second amplifier is set to be large,
• wherein the controller performs a first decay operation for increasing the first gain in accordance with a decrease in the detected level of the digital audio signal before the signal processing after the first gain is reduced, and
• wherein the second amplifier performs a second decay operation for increasing the second gain in accordance with a decrease in the detected level of the digital audio signal after the signal processing after the second gain is reduced and stops performing the second decay operation while the controller performs the first decay operation.

A signal processing device comprising:

• a first amplifier that amplifies a level of an analog audio signal input from an external source with a first gain whose value is variable;
• a converter that converts the analog audio signal amplified by the first amplifier into a digital audio signal;
• a signal processor that performs signal processing for controlling tone of the digital audio signal;
• a controller that detects a level of the digital audio signal before the signal processing and controls the value of the first gain in accordance with the detected level of the digital audio signal before the signal processing;
• and
• a second amplifier that detects a level of the digital audio signal after the signal processing, determines a second gain in accordance with the detected level of the digital audio signal after the signal processing and the first gain, and amplifies the digital audio signal after the signal processing with the second gain,
• wherein the second amplifier generates an output signal for audio equipment that is not included in the signal processing device itself,
• wherein the controller performs a first decay operation for increasing the first gain in accordance with a decrease in the detected level of the digital audio signal before the signal processing after the first gain is reduced, and
• wherein the second amplifier performs a second decay operation for increasing the second gain in accordance with a decrease in the detected level of the digital audio signal after the signal processing after the second gain is reduced and stops performing the second decay operation while the controller performs the first decay operation.