Other hardware: Difference between revisions

From Hydrogenaudio Knowledgebase
No edit summary
Line 18: Line 18:
Vendor extension codecs:
Vendor extension codecs:
* AptX, LDAC, LLDC: in general lower complexity but higher bitrate (still within BT limits) than AAC, transparency possible; AptX and LDAC has wide support
* AptX, LDAC, LLDC: in general lower complexity but higher bitrate (still within BT limits) than AAC, transparency possible; AptX and LDAC has wide support
* FastStream: Qualcomm's bidirectional SBC variant, providing a mono back channel


Bitrate is limited by bluetooth link. A maximum of 2 channels is enforced for all codecs: this is a headphone protocol, not a speaker protocol. No back-channel is defined.
Bitrate is limited by bluetooth link. For all relevant codecs, there is a maximum limit of 2 channels: this is a headphone protocol, not a speaker protocol. Microphone-back channel is not available except in FastStream.


=== Sub Band Codec ===
=== Sub Band Codec ===
Line 28: Line 29:


Reference: [https://www.bluetooth.org/foundry/adopters/document/A2DP_Spec_V1_0/en/ BLUETOOTH Advanced Audio Distribution Profile 1.0]
Reference: [https://www.bluetooth.org/foundry/adopters/document/A2DP_Spec_V1_0/en/ BLUETOOTH Advanced Audio Distribution Profile 1.0]
== Bluetooth (HSP/HFP) ==
This is the mode with mono input and output, both at voice sample rates. Only very crude encodings (CVSD, PCM, optionally SBC 16KHz) are supported, so do not expect audio quality.


== Headphones ==
== Headphones ==

Revision as of 10:52, 6 July 2023

Bluetooth (A2DP)

Advanced Audio Distribution Profile (A2DP)

Standard baseline codecs:

  • Sub Band Codec (SBC) – not great
  • LC3 – the new baseline of Bleutooth 5.1. About Opus level, allegedly

Standard optional codecs:

  • MPEG-1,2 Audio: = MP3, almost never used
  • AAC: relatively good decode support, transparency possible at bluetooth bitrates, but latency can be an issue
  • ATRAC: never used

Vendor extension codecs:

  • AptX, LDAC, LLDC: in general lower complexity but higher bitrate (still within BT limits) than AAC, transparency possible; AptX and LDAC has wide support
  • FastStream: Qualcomm's bidirectional SBC variant, providing a mono back channel

Bitrate is limited by bluetooth link. For all relevant codecs, there is a maximum limit of 2 channels: this is a headphone protocol, not a speaker protocol. Microphone-back channel is not available except in FastStream.

Sub Band Codec

  • Sampling Frequency - 16000, 32000, 44100, 48000 (some are optional, see references)
  • Channel Mode - mono, dual channel, stereo, joint stereo

The bitrate used for CD-quality () audio is 229 kbps and 328 kbps for middle and high quality, respectively.

Reference: BLUETOOTH Advanced Audio Distribution Profile 1.0

Bluetooth (HSP/HFP)

This is the mode with mono input and output, both at voice sample rates. Only very crude encodings (CVSD, PCM, optionally SBC 16KHz) are supported, so do not expect audio quality.

Headphones

Some Styles (smallest to largest)

  • In the ear - outputs directly into the ear canal
  • Earbuds - sits in the outer ear
  • Supra-aural - sits on the ear
  • circumaural - completely cover the ear

Terminology used for comparing headphones

  • Noise Cancelling
    • active
    • passive
  • Frequency response - The range of frequencies the headphones can reproduce
  • Impedance - Doesn't mean much by itself, but in general, impedence should be matched across a system.
  • SPL@1kHz, 1V rms - Sound Pressure Level. How efficient the unit converts electrical energy to sound energy.
  • Neodymium - The magnet of choice for high end headphones.

Popular Headphones

  • Sub $30
  • Sub $100
  • $100 - $300
  • $300+