Sound Blaster Roar SR20A White Paper – Evolution, Concept and Tech Overview
10/7/2014 P
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AptX Codec Support
What is aptX? Originally developed for use in the professional audio and broadcasting
sectors, aptX
is a real-time digital audio data reduction system that compresses linear
audio samples by a factor of 4:1 with no perceptible audible degradation and with
negligible delay.
Why aptX? To manage the transfer of stereo audio, the
Bluetooth
Special Interest Group
(SIG) has ratified a profile known as A2DP (Advanced Audio Distribution Profile).
Bluetooth
stipulates maximum available bandwidth for A2DP at 768kbps. So for high
quality stereo music, it is necessary to use some form of audio coding to reduce the
required data rates.
Take for example, a 16-bit stereo (regarded as entry level for audio systems) with a
minimum sample rate of 44.1 kHz to match the venerable audio CD:
Dynamic Range:
16 Bit Digital Audio = 20Log10 (2
16
) = 96.32 dB
20 Bit = 120.4 dB etc….
Taking CD quality as the benchmark, 16-bit, 44.1 kHz has a dynamic range of 96dB.
To achieve this level of dynamic range in bandwidth limited applications, it will be
necessary to use at least 16-bit audio as the raw input and then a compression technology
that can reproduce virtually all the dynamic range at the output.
Uncompressed audio utilizes a bandwidth of 1.411Mbps for CD quality and for the vast
majority of wireless applications, full bandwidth is simply impractical. Issues of design,
efficiency, power optimization and error resilience will all put pressure on available data
rates.
AptX uses advanced ADPCM principles which encode the entire frequency range of the
audio. MP3 uses psychoacoustic techniques, which throw away audio they deem
unimportant, SBC reproduces limited audio bandwidth.
So what is the bandwith of aptX? Here’s the breakdown:
CD 16 bit /44.1kHz
20Hz- 22kHz
aptX 20Hz-22kHz
SBC
20Hz-17kHz
