Audio Hardware

Created: 5/12/2020Lasted updated:5/12/2020

Introduction

Audio hardware is responsible to generate, receive, and process audio signals to and from the main processor. Audio signals are in two forms, analog and digital.

Note: Analog signals are real world signal represented in sound pressure and voltage: however, in this context, we limit the analog definition to voltage.

Background

Analog Voltage Levels

Line levels: line-in/line out operates at 0.316 Vrms level.
Microphone level: analog microphone signal operates between 1mV to 10 mV

Audio Ports

Line in/out: audio in/out port
- connect to device such as CD player, Mixer, etc. typically found on PC
Headphone Line out: audio out port
- connect to headphone or earphone jack
Mic in: microphone audio input port used for recording, voice recognition, etc.
Headphone jack with built-in mic: audio port supports both headphone line out and and microphone in.

Audio Connector

Line-in/out audio Jack
- 3.5 mm jack stereo audio is common.

Audio Playback Device

Line out Amplifier
- It's a audio power amplifier that sends line level signal to an audio jack to external audio devices
- In typical consumer electronics, a CODEC chip generates line out voltage
Built-in Speaker Amplifier
- A speaker amplifier is used to convert line out signal to necessory speaker level signal to drive a speaker driver.
- In consumer electronics, high efficient digital Class-D amplifier is used to drive a speaker outout.
Speakers (also known as driver or transducer)

Audio Capture Device

Microphone
- it's a electroacoustic transducer that converts acoustic signal to electrical signal.
Mic in pre-amplifier
- analog microphone has low output voltage that needs to amplified to a line level before digital conversion.
- In consumer electronics, mic in is connected to the Mic-in of the CODEC chip which has internal amplifier.

Audio Processing Device

Digital Signal Processor
- Main Components
- Main Functions:
  - Audio pre-processing
    - Filtering, noise reduction, sample rate conversion, dynamic range control, amplification etc.
  - Audio post-processing
    - Dynamic Range Compression (i.loudness control)
Codec
- It's audio device that has function of both encoding an audio from analog line/mic in to digital audio and decode a digital audio to analog line out.
- It contains both control and data interface to the main processor.

Detailed Analysis

Consumer electronics mostly contains headphone line-out jack and built-in microphones with embedded CODEC and digital amplifier for built-in speakers.

See Audio System for an example block diagram.

Most of built-in microphones in electronics are digital MEMS mic which direct outputs a digital audio format , PDM is standard.

Most of built-in speakers is driven by Class-D amplifier low cost and high efficiency.

PC has dedicated line-in/out ports, microphone in ports that is processed by a soundcard. Soundcard contains a mainly DSP, CODEC, and audio ports.

See Soundcard for an example.

Q&A

What are the main audio hardware?

Transducers, ADC, DAC, CODEC and DSP.

Summary and Conclusion

Line level is operates at higher voltage level
Mic level operates at lower voltage level
CODEC does analog to digital (ADC) and digital to analog conversion (DAC)
- ADC is categorized as encoding and DAC is categorized as decoding
DSP does complex mixing, pre/post audio processing.
Class-D amplifier is common for built-in speakers
MEMS Microphone is common for built-in microphones.

Audio hardware works together to generate, receive, and process audio signals.

Audio Hardware

Introduction

Background

Detailed Analysis

Q&A

Summary and Conclusion

Further Reading and Practice