Other hardware: Difference between revisions

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* 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


Bitrate is limited by bluetooth link
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.


=== Sub Band Codec ===
=== Sub Band Codec ===

Revision as of 10:47, 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

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.

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

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+