Audio Hardware
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.
- Low frequency band
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
- Equalization (i.e Sound effect)
- Dynamic Range Compression (i.loudness control)
- Audio pre-processing
- Main Components
- 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.
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