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Now Live: Digital Assistant for Hardware Development
Created: 5/12/2020
Introduction
Introduction
Audio hardware is responsible for generating, receiving, and processing audio signals, which can be either analog or digital. In this context, we limit the definition of analog signals to voltage levels.
Background
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: Connects to devices like CD players and mixers; typically found on PCs.
Headphone Line Out: Connects to headphone or earphone jacks.
Mic In: Used for recording, voice recognition, etc.
Headphone Jack with Built-In Mic: Supports both headphone line-out and microphone in.
Audio Connector
Commonly, a 3.5 mm stereo audio jack is used for line-in/out.
Audio Playback Device
Line-Out Amplifier
Sends line-level signals to external audio devices. In consumer electronics, a CODEC chip generates the line-out voltage.
Built-in Speaker Amplifier
Converts line-out signals to drive a speaker.
High efficient digital Class-D amplifiers are commonly used in consumer electronics.
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 Devices
For practical design example see this article: https://www.hwe.design/system-design/audio-system/audio-capture
Microphone
An electroacoustic transducer converting acoustic signals to electrical ones.
Mic-in Pre-amplifier
Amplifies the low-output voltage from analog microphones to line level before digitization.
In consumer electronics, mic in is connected to the Mic-in of the CODEC chip which has internal amplifier.
Audio Processing Device
For practical design excample please this article: https://www.hwe.design/system-design/audio-system/audio-playback
Digital Signal Processor (DSP)
Main components include Instruction RAM, Data RAM, and a Compute Engine.
Typical architectures use Cadence Tensilica Based DSPs with HIFI3/HIFI4 instruction sets.
Main Functions of Audio Processing on DSP
Pre-Processing
Filtering: Removes unwanted frequency components from the audio signal.
Example: DC cutting is used to remove the bias inherent to microphone hardware. This is implemented as a high-pass filter with a cutoff frequency near DC, such as 10 Hz.
Noise Reduction: Minimizes background and ambient noise.
Sample Rate Conversion: Adjusts the sample rate for compatibility or quality.
Dynamic Range Control: Balances the loudness of different audio elements.
Amplification: Increases the volume level of the audio signal.
Post-Processing
Dynamic Range Compression: Controls loudness to maintain a consistent audio level.
Equalization: Modifies the frequency response for desired sound effects.
Parametric Equalizer (PEQ): Allows for precise frequency and Q-factor adjustments.
Graphic Equalizer (GEQ): Modifies multiple frequency bands simultaneously.
Constant Q: Equalization that maintains a consistent bandwidth.
⅓ Octave Band: Equalization using third-octave frequency bands.
Crossover: Divides the audio signal into various frequency bands for different drivers (speakers).
Downmixing: Converts multi-channel audio, like 5.1 surround sound, to a 2-channel stereo.
Upmixing: Expands 2-channel audio to a multi-channel format, like 5.1 surround sound.
Additional Features
Volume Control: Adjusts the overall loudness level.
Surround Sound: Provides an immersive audio experience by utilizing multiple speakers.
Mixer: Combines system sounds with various audio streams for a unified output
Codec (Coder-Decoder)
A CODEC is an audio device designed to perform two main functions: encoding analog audio signals from line-in or microphone inputs to digital form, and decoding digital audio back to analog form for line-out. It interfaces with the main processor through both control and data channels.
Detailed Analysis
Detailed Analysis
Consumer Electronics: These devices often feature headphone line-out jacks and built-in microphones. The CODEC and digital amplifier are generally embedded in the system for built-in speakers. For an illustrative example, refer to Audio System block diagram
Digital MEMS Microphones: Most built-in microphones in consumer electronics are digital MEMS mics that output audio in a standard digital format, typically Pulse Density Modulation (PDM).
Class-D Amplifiers: These are commonly used to drive built-in speakers due to their low cost and high efficiency.
Personal Computers: PCs usually have dedicated line-in/out and microphone-in ports. These are processed by a sound card, which primarily contains a DSP, CODEC, and various audio ports. For an illustrative example, refer to Soundcard block diagram for an example.
Q&A
Q&A
What are the main components in audio hardware?
The primary components include Transducers, ADC (Analog-to-Digital Converters), DAC (Digital-to-Analog Converters), CODEC, and DSP (Digital Signal Processors).
Summary and Conclusion
Summary and Conclusion
Voltage Levels: Line levels operate at higher voltage levels, while microphone levels are at lower voltages.
Encoding and Decoding: CODECs are responsible for both ADC and DAC functions. ADC is generally considered as encoding, and DAC as decoding.
DSP Functions: Digital Signal Processors handle complex tasks like mixing and pre/post audio processing.
Common Hardware: Class-D amplifiers are prevalent in built-in speakers, and MEMS microphones are a standard for built-in microphones.
Overall, audio hardware components work cohesively to generate, receive, and process audio signals.
Further Reading and Practice
Further Reading and Practice
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