Other hardware: Difference between revisions

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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+

@@ Line 18: / Line 18: @@
 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. 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 ===
@@ Line 28: / Line 29: @@
 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 ==