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)
      • Mono/Stereo/Multi-Channel speaker systems
      • Driver Types
        • Low frequency band
          • Subwoofer [<200 Hz]
        • Mid range frequency band
          • Woofer [20 to 2kHz]
        • High frequency band
          • Tweeter [2kHz to 20kHz]
        • Full Range band
          • Full range speaker [~ 60/100 Hz to 18 kHz]
          • This commonly found in consumer electronics such as phone, TV, smart speakers, etc.

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
        • Instruction Ram (IRAM)
        • Data Ram (DRAM)
        • Compute Engine
          • Typical architecture are Cadence Tensilica Based DSP with HIFI3/ HIFI4 instruction sets.
    • 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)
            • Equalization (i.e Sound effect)
              • PEQ
              • GEQ
                • Constant Q
                • â…“ octave band
            • Crossover (i.e frequency slicing for different drivers).
            • Down Mixing
              • 5.1 Surround Sound to 2 Ch
            • Up Mixing
              • 2 Ch to 5.1 s
              • Volume Control
              • Surround Sound
            • Mixer
              • Mix system sound with audio stream
  • 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.

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.

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.

Further Reading and Practice

"Line Levels", https://en.wikipedia.org/wiki/Line_level

"Mic level and Line level, what do they mean", https://service.shure.com/s/article/mic-level-and-line-level-what-do-they-mean?language=en_US

"Headphone Jack Detect and Operation Example ", https://statics.cirrus.com/pubs/appNote/WAN0196.pdf

"CODEC Evaluation Connection Examples", https://statics.cirrus.com/pubs/manual/WM8731L_M_Example_Configurations.pdf