MCPC TR-027
Bluetooth SBC Parameters
Recommendation
Technical Reference
Version 1.0 English
19th Feb. 2020

Mobile Computing Promotion ConsortiumHistoryDate
19th Feb. 2020

Version1.0

Comments
Adopted by the MCPC ATA SWG

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Disclaimer:This document is intended to provide standard specifications, recommended specifications, etc. onmobile computing. Mobile Computing Promotion Consortium (hereafter MCPC) shall not be liable forany damages or infringements of patents or other rights of third parties arising out of the use of thisdocument. This document shall not be construed to grant (a) license(s) under any rights held by MCPCor third parties.

©Copyright 2020 Mobile Computing Promotion Consortium (MCPC)MCPC TR-027 Bluetooth SBC Parameters Recommendation Technical Reference Version 1.0

Contributors
Itsuo SakaiAllion Japan Inc.

Hiroyuki Morimoto

Mitsubishi Electric Corporation

Masahiko Seki

Sony Home Entertainment & Sound Products Inc.

Toshiya Tamura

FUJITSU CONNECTED TECHNOLOGIES LIMITED

Mitsuyoshi Yasuda

Sony Mobile Communications Inc.

Akio Konishi

TAIYO YUDEN CO., LTD.

Sadamitsu Kanamori

Renesas Electronics Corporation

Souichi Saitou

DENSO Corporation

Kazuhiro Hirose

Clarion Co., Ltd.

Yasushi Otomo

ALPS ALPINE CO., LTD.

Shinichi Miyano

Visteon Japan Ltd.

Tadashi Hanada

Hosiden Corporation

Masahiro Sato

Hosiden Corporation

Hidenori Okawa

JVCKENWOOD Corporation

Fusako Inotsume

PIONEER CORPORATION

Yasuho Egawa

Mobile Computing Promotion Consortium2©Copyright 2020 Mobile Computing Promotion Consortium (MCPC)MCPC TR-027 Bluetooth SBC Parameters Recommendation Technical Reference Version 1.0

Table of ContentsIntroduction .................................................................................................................... 4
1.1 Scope .................................................................................................................................... 4

Overview of proposal .................................................................................................... 5
2.1 Proposal A: New SBC encoder settings for EDR ................................................................... 5
2.2 Proposal B: Media payload forming to fit to ACL packet ......................................................... 5
2.3 Proposal C: SRC device configuration for SBC encoder settings ........................................... 5

Coverage of requirements ............................................................................................ 6Problem definition ......................................................................................................... 7Description ..................................................................................................................... 85.1 Proposal A: New SBC codec settings for EDR ..................................................................... 125.2 Proposal B: Media payload forming to fit to ACL packet ....................................................... 125.3 Proposal C: SRC device configuration for SBC codec settings ............................................ 123

©Copyright 2020 Mobile Computing Promotion Consortium (MCPC)MCPC TR-027 Bluetooth SBC Parameters Recommendation Technical Reference Version 1.0Introduction
1.1 ScopeBluetooth entertainment audio has become quite popular. For the audio streaming, SBC (Sub BandCodec) is now widely used as mandatory codec with the recommended encoder settings (especiallyBitpool value) described in ‘Advanced Audio Distribution Profile (A2DP) v1.3.2’ as quoted asfollowings.

Those SBC encoder settings are optimized for Bluetooth Classic BR (Basic Rate) core although it
becomes major to use EDR (Enhanced Data Rate). The issue is that the SBC encoder settings
optimized for BR is nevertheless applied to EDR in most case. It causes inefficiency of air use totransfer audio data on EDR and SBC’s codec rate is suppressed in lower level of which audiophile
complains.
To solve the issue, this document newly recommends to use optimized SBC codec settings for EDR
in place of Table 4.7 in A2DP v1.3.2’. It makes audio quality better without special effort.

4©Copyright 2020 Mobile Computing Promotion Consortium (MCPC)MCPC TR-027 Bluetooth SBC Parameters Recommendation Technical Reference Version 1.0

Overview of proposal
This Technical Reference document newly proposes ‘Recommendation of SBC parameters setting in theSRC for EDR’ and Media payload forming manner to enable efficient SBC frames stuffing into single
2-DH5 packet that is essential for the recommendation. This is an extension of the existing
recommendation in ‘Advanced Audio Distribution v1.3.2’ (Table 4.7) that is optimized for BR.
Additionally, it also recommends that SRC supports selection menu of the SBC settings in association
with the proposal.

2.1 Proposal A: New SBC encoder settings for EDR
Table 5.1 Recommended sets of SBC parameters in the SRC for EDR

2.2 Proposal B: Media payload forming to fit to ACL packet
Recommendation of the most efficient media frame forming to fit to the ACL packet for EDR that is to be
applied with Proposal A

2.3 Proposal C: SRC device configuration for SBC encoder settings
Additional recommendation of SBC setting selection menu in SRC

5©Copyright 2020 Mobile Computing Promotion Consortium (MCPC)MCPC TR-027 Bluetooth SBC Parameters Recommendation Technical Reference Version 1.0

Coverage of requirements
A2DP_v.1.0 or later (The latest version is 1.3.2)
4.3 SBC
5.2.1 Maximum Transmission Unit
5.5 Link Controller Interoperability Requirements

6©Copyright 2020 Mobile Computing Promotion Consortium (MCPC)MCPC TR-027 Bluetooth SBC Parameters Recommendation Technical Reference Version 1.0

Problem definition
The low audio quality of the SBC codec is caused by artificial limitations of all current Bluetooth stacks
and SNKs’ configuration following the recommended sets of SBC parameters. But this limitation canbe circumvented because SBC codec supports flexible parameters which can be selected by SRC.
Almost of existing SRC use the recommended higher quality audio parameters specified in Table 4.7(328kbps or 345kbps, Joint Stereo). However, the recommended settings are not optimal for EDR
devices in terms of audio quality and efficiency of air time which is occupied by audio streaming
packets. The efficiency of air time affects coexistence performance and the number ofretransmissions. More capacity for retransmissions (to make the audio streaming more reliable)
provide more capacity for other applications in multi-profile/device scenario.
If new recommendation for EDR device is added in A2DP specification [1], it will enhance audio qualityof SBC.

Figure 4.1: Frequency Response of Original and SBC 328kbps

7©Copyright 2020 Mobile Computing Promotion Consortium (MCPC)MCPC TR-027 Bluetooth SBC Parameters Recommendation Technical Reference Version 1.0

Description
SBC requires several different parameters to be negotiated during the connection setup phase.
Followings are those parameters with all of mandatory elements to be supported in SNK which ‘A2DP
v1.3.2’ specifies. (SNK is required to support any combinations of these parameters except for 16kHz
and 32kHz sampling frequency. SRC is allowed to implement only a part of them.)-Channel Mode: Joint Stereo, Stereo, Dual Channel, Mono
Subbands: 4 or 8
Block Length: 4, 8, 12, 16
Allocation Method: Loudness, SNR
Bitpool Value: 2 -250 (Allowed range; though usually seen 2-53)
Sampling Frequency: 44.1kHz, 48kHz, 16kHz (Optional for SNK), 32kHz (Optional for SNK)
Majority of existing Bluetooth stacks usually negotiate the following profile: Joint Stereo, 8 bands, 16blocks, Loudness, bitpool 53. This profile encodes 44.1kHz audio with a bitrate of 328kbps, as it isalong recommendation in Table 4.7 of A2DP specification [1]. Though it is suitable for BR, not always
best for EDR. An example is described below.
In the case that the same profile as BR is applied to EDR and SNK’s MTU size for L2CAP media
transport channel is 672 octets, five SBC frames are packed in a 2-DH5 packet. As SBC frame lengthis 119 octets and AVDTP header is 14 octets, 63 octets are wasted. (Please refer to “12.9 Calculationof Bit Rate and Frame Length in A2DP specification [1]” for frame length)

Figire.5.1: Transmission Efficiency example 1
As shown above, 63 octets room remains for a full 2-DH5 packet capacity in this case.
If the bitpool value 59 is applied, the SBC frame length is 131 octets and the wasted bytes aresuppressed as 4 octets. From the perspective of the data transfer capability, the air resource
consumption for bitpool value 59 is the same as that of 53. Since, the higher bitpool value provides
the higher bitrate, it means that the better audio quality is available under the same air condition.
Therefore, bitpool value 59 provides more efficient and better audio quality than 53.

Figure 5.2 Transmission Efficiency example 2Majority of SNK seems to limit maximum bitpool value as 53, which prevents bitrates higher than
328kbps to be used with the common 44.1kHz Joint Stereo, 8 subbands, 16 blocks length.
But the bitrate is also affected by other parameters.

8©Copyright 2020 Mobile Computing Promotion Consortium (MCPC)MCPC TR-027 Bluetooth SBC Parameters Recommendation Technical Reference Version 1.0
For example, Subband 4 can get almost doubled bitrate than Subband 8 at the same bitpool value.

Figure 5.3: Bit Rate to the corresponding bit pool value (Subband 8 and 4)
Regarding the number of subband, 8 is better audio quality when the bitrate is lower. On the other
hand 4 is better audio quality when the bitrate is higher. Because higher bitrate can allocate more bits
to all bands and smaller number of bands can reduce filter bank aliasing noise, which is inherent toSBC.
Subjective evaluation showed that the cross point bitrate for stereo was between 400 and 450kbps.

Figure 5.4: Audio Quality to Bit Rate (Subband 8 and 4)

9©Copyright 2020 Mobile Computing Promotion Consortium (MCPC)MCPC TR-027 Bluetooth SBC Parameters Recommendation Technical Reference Version 1.0
Filter bank aliasing (Sine wave 1kHz)

Figure 5.5: Filter Bank Aliasing NoiseThe following example is air time to bit rate (bitpool) for subband 8 and 4 in case of EDR 2Mbps and44.1kHz sampling frequency.
More efficient bitpool values in combination with appropriate number of the subband for EDR 2Mbps
are 59 (361kbps) with subband 8, 75 (449kbps) with sububand 8 or 36 (444kbps) with subband4, and42 (510kbps) with subband 4.
In this recommendation, 36 (444kbps) with subband 4 instead of 75 (449kbps) with sububand 8 istaken because the lower bitpool value can be accepted by majority of SNK whose maximum bitpool
value is 53.

Figure 5.6: Air Time to SBC Bit Rate

10©Copyright 2020 Mobile Computing Promotion Consortium (MCPC)MCPC TR-027 Bluetooth SBC Parameters Recommendation Technical Reference Version 1.0
SBC 328kbps completely cuts off upper frequencies often. Bitrate 510kbps saves the entire frequency
range without cutting off.

Figure 5.7: Improved Frequency Response11©Copyright 2020 Mobile Computing Promotion Consortium (MCPC)MCPC TR-027 Bluetooth SBC Parameters Recommendation Technical Reference Version 1.0

5.1 Proposal A: New SBC codec settings for EDRThe following table is “Recommended sets of SBC parameters in the SRC for EDR” additionally to theexisting recommendation described in Table 4.7 of A2DP Specification [1].
The decoder of the SNK should support 59 as the Maximum Bitpool Value at a minimum.

EDR
Low Quality

EDR
Middle Quality

EDR
High Quality

SBC encoder settings*
Joint Stereo
Joint Stereo
Joint Stereo
Sampling frequency (kHz)
44.1
48
44.1
48
44.1
48
Bitpool value
59
59
36
32
42
36
Resulting frame length (bytes)
131131
81
7393
81
Resulting bit rate (kb/s)
361
393
444435510483Subbands
884444*Other settings: Block length = 16, Allocation method = Loudness or SNR
Table 5.1: Recommended sets of SBC parameters in the SRC (EDR)

5.2 Proposal B: Media payload forming to fit to ACL packet
SRC recognizes if the SNK supports BR only or EDR also in LMP supported features.
SRC should determine the SBC encoder settings depending that SNK supports BR only or EDR also.
In case both SRC and SNK support EDR, SRC should use EDR 2Mbps for media transport channel
and use 2-DH5 packet for transporting media even when SNK supports EDR 3Mbps and 3-DH packet.
SRC should form media payload within the length of 672 octets even when SNK declares that theMTU size for media transport channel is greater than 672 octets. 672 octets fit to the payload size of2-DH5 packet.
The minimum MTU of L2CAP for media transport channel in case of EDR should be 672 bytes.
(5.2.1 Maximum Transmission Unit in A2DP specification [1] specifies that the minimum MTU is 335
bytes).
All 2-DH and 2-DM packets should be supported for EDR in both SNK and SRC in addition to DH3,DM3, DH5, and DM5 which are stated in 5.5 Link Controller Interoperability Requirements of A2DP
specification [1].

5.3 Proposal C: SRC device configuration for SBC codec settings
SRC should provide the selection menu of bitrate for each paired SNK to be interoperable with any
SNK existing in market. (Not all existing SNK may be able to decode new recommended sets of SBC
parameters). At least one possible BR recommendations (Table 4.7 in A2DP specification [1]) and one
possible EDR recommendation shown in above table (Table 5.1) should be included in the selectionmenu. If SRC is not able to provide the selection menu, the recommendation for BR may be adopted.

12©Copyright 2020 Mobile Computing Promotion Consortium (MCPC)MCPC TR-027 Bluetooth SBC Parameters Recommendation Technical Reference Version 1.0

References[1] A2DP specification 1.0 or later from www.bluetooth.com

13©Copyright 2020 Mobile Computing Promotion Consortium (MCPC)MCPC TR-027 Bluetooth SBC Parameters Recommendation Technical Reference Version 1.0

MCPC TR-027 ver.1.0 English
Bluetooth SBC Parameters Recommendation Technical Reference

19th February 2020

Mobile Computing Promotion Consortium
Hasegawa Green Bldg. 5-12 Shiba-Koen 3-chome, Minato-ku, Tokyo, 105-0011 Japan
Copying part or everything in this document without permission becomes copyright and bookmaker's
infringements of right. The reprint from this document is a principle prohibition. Please obtain thepermission of mobile computing promotion consortium (MCPC) when reprinting in other books, etc.

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