Project Bar-B-Q 2018 report section 6

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The Twenty-third Annual Interactive Audio Conference PROJECT BAR-B-Q 2018

Group Report:
A World Without 3.5mm: Transport Features,
Guidelines, and Opportunities

Participants: A.K.A. "Hit the Road Jack"

Abdul (Rahman) Ismail, Intel Corp

David Dashefsky, Analog Devices

Morris Yeh, Dialog Semiconductor Inc.

Albert Yong, Bowers & Wilkins

Roy Goh, Microsoft

Jan-Paul Huijser, NXP Semiconductors

Nick Ray, Microsoft Corp

Miguel Sanchez, Cirrus Logic, Inc.

Adeel Aslam, Intel

Facilitator: Linda Law, Project Bar-B-Q

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Problem Statement

In a world without 3.5mm, there is no gold standard for what should come next. The widely accepted Bluetooth and USB-C solutions have inherent limitations - including but not limited to interoperability, power, and audio fidelity. In addition, a transport-agnostic audio standard does not exist that delivers baseline audio fidelity.

Solution Statement

Our project aims to flesh out a transport-agnostic audio feature set. We identified gaps in existing transport solutions (Bluetooth, WiFi, and USB-C) and created a requirements document to address them. We also created development guidelines ensuring baseline audio fidelity. Lastly, we suggested opportunities for differentiation for developers to provide added value in the new recommendation.

Expanded problem statement

We identify the following criteria as areas of improvement in existing transport solutions:

Latency
Volume control
Maximizing bandwidth utilization
Minimal power consumption
Synchronization
Feature discoverability (transport and device)
# of channels
Compatibility/interoperability
Link stability
Control
Bidirectional audio
Security
Multi-endpoint
Multi-source
Power modes
Cost
Quality of service
Association of non-audio communication
Range
Noise
Ease-of-use

Requirements

Transport-agnostic Audio Feature Set

Latency
- Transport: min X
- Device: min Y
- System latency is out-of-scope
- Minimum latency requirements vary by use case
Volume control
- Avoid loss of quality
  - Stream-dependent adaptation
- Volume ceiling
- Volume persistence across sources/endpoints
- SPL-based control
- Adaptive SPL attenuation
Maximizing bandwidth utilization
- Querying for:
  - Max bandwidth
  - Avg bandwidth
  - Variable bandwidth
- Bandwidth reservation
Minimal power consumption
- (Host) Target of X watts
  - Parity within 10% of 3.5mm
- (Device) Target of Y watts
  - 24 hours
Synchronization
- Channel sync
  - Stereo sync across multiple devices: Target of <1us
  - Stereo sync on single device: Target of <1us
  - Time of Flight reporting per-endpoint
  - Timestamping
  - Round-trip delay reporting
- A/V sync
Feature discoverability (transport and device)
- Reporting:
  - Terminal type
  - Audio processing capability
  - Transport characteristics
  - Format capabilities
  - Volume capabilities
  - Latency
    - Per-feature
# of channels
- Channels and/or data slots i.e. high speed data
Compatibility/interoperability
- Minimal feature set targets
  - Encode/decode
  - Bit resolution
  - Sampling frequency
  - Format capabilities
  - Control set
    - Volume/Mute
    - Media controls (Play/Pause/Next/Prev)
- Proprietary extensibility
Link stability
- Dropout mitigation
Control
- Audio processing disablement
- Bidirectional media (2 capture, 2 render)
Bidirectional audio
- Incoming to host:
  - Post-process reference signal
  - ANC reference signal
  - Recording
Security
- Stream interception prevention
  - Wireless: encryption
  - Wired: N/A
Multi-endpoint
- Broadcast
- Aggregation
Multi-source
- Dynamic source switching
- Intelligent source ranking
- Public barge-in i.e. accept incoming public streams
Power modes
- Power/perf gradience
- Low power states
- Auto sleep/wake
Cost
- Price point within 25% of an equivalent product
Quality of service
- Condition-adaptive audio codec
- Glitching/artifacts
Association of non-audio communication
- Sensory information
- Per-endpoint characteristics
  - Geometry
  - Sensitivity
  - Non-audio control (to host) without interrupting audio
  - Non-audio control (to device) without interrupting audio
Range
- Wireless: 10ft
Noise
- SNR
Ease-of-use
- Pairing - no hassle
  - Multiple device pairing
  - Per-user settings
  - Per-device settings
- Sufficient data to host to enable plug-n-play

Development Guidelines

Goal: Create a set of development guidelines ensuring baseline audio fidelity.

Latency
- [48khz & 24 bits] Target: max of 1ms
  - Currently max may not be attainable with error correction implementation
  - Higher sample rate and frequency may sacrifice latency
Volume control
- Avoid loss of quality: maximize signal-to-noise ratio based on capabilities of underlying transport.
  - Stream-dependent adaptation:
    - Recalculate transmission channel whenever a stream is destroyed or created.
    - Adopt master volume in end node.
- Adaptive SPL attenuation: don't do it in the host.
- SPL-based volume control: transport supports host/device volume capabilities negotiation

Goal is to Avoid loss of quality: maximize signal-to-noise ratio based on capabilities of underlying transport. Example of this concept is given in below slides

Maximizing bandwidth utilization
- Bandwidth reservation: nice-to-have
Minimal power consumption: efficient bandwidth utilization and minimal bandwidth reservation provides power savings.
Synchronization
- Channel sync:
  - Ensure stereo sync across multiple devices: Target of <1us
  - Ensure stereo sync on single device: Target of <1us
  - Adopt 802.1.as:
    - Time of Flight reporting per-endpoint
    - Timestamping
    - Round-trip delay reporting
- A/V sync
  - [ACTION] Albert to check AVB requirements
# of channels
- Channels and/or data slots i.e. high speed data
- [ACTION] Jan-Paul to investigate
Compatibility/interoperability
- Minimal feature set
  - Support lossless encode/decode
  - Targets
    - Bit resolution: >=24bits
    - Sampling frequency: >=48khz
  - Format capabilities: PCM or lossless compression
Link stability
- Implement dropout mitigation mechanisms while minimizing latency:
  - Retransmission
  - Error correction
  - Error concealment
Power modes
- Power/perf gradience:
  - Provide intelligent or manual degradation of fidelity balanced against power needs.
Quality of service
- Condition-adaptive audio codec
  - Implement dropout mitigation by only providing necessary fidelity informed by condition detection on host.
- Glitching/artifacts
  - Implement seamless mode/settings changes to avoid glitching/artifacts.
Association of non-audio communication
- Unload bandwidth reservation for non-audio communication when not in use.
Range
- Ensure sufficient power transmission to maintain baseline fidelity up to specified targets.

Differentiation

Situational reduced fidelity for decreased power consumption
Latency
- Ultra-low
Minimal power consumption
- Ultra-low
Synchronization
- Ultra-low drift between aggregated/broadcasted devices
Seamless multi-transport support
# of channels
- More
Broad feature support
- EQ
- Surround Sound
- Bass Boost
- Spatialized Audio
- ANC
- etc.
Link stability
- Enhanced
Bidirectional audio
Multi-endpoint
- More
Multi-source
- More
Power modes
Quality of service
- Condition-adaptive
Support for association of non-audio communication
- Vital signs monitoring
- Head tracking
- etc
Range
- Wireless: farther
Noise
- Higher SNR
Ease-of-use
- Easy pairing
- Plug-n-play

Other reference material

Transport-agnostic Audio Feature Set	Bluetooth	USB-C	WiFi	3.5mm
Latency
Transport: 1ms	No	Yes	No	Yes
Volume control	Yes	Yes	Yes	Yes
Avoid loss of quality
Volume ceiling
Volume persistence across sources/endpoints
SPL-based control
Stream-dependent adaptation
Adaptive SPL attenuation
Maximizing bandwidth utilization
Querying for:
Max bandwidth	Yes	Yes	Yes	N/A
Avg bandwidth	Yes	Yes	Yes	N/A
Variable bandwidth	Yes	N/A	Yes	N/A
Bandwidth reservation	Yes	Yes	?	N/A
Minimal power consumption
(Host) Target of X watts
Parity within 10% of 3.5mm	?	No	No	Yes
(Device) Target of Y watts
24 hours	Some	N/A	No?	Yes
Synchronization
Channel sync
Stereo sync (single device): Target of <1us	Yes	Yes	?	Yes
Stereo sync (multiple devices): Target of <1us	Future	Possible	?	Yes
Time of Flight reporting per-endpoint	Possible	Possible	?	N/A
Timestamping	Possible	Possible	?	N/A
Round-trip delay reporting	No	Yes	?	N/A
A/V sync	Yes	Possible	Yes	Yes
Feature discoverability (transport and device)
Reporting:
Terminal type	Yes	Yes	?	No
Audio processing capability	No	Yes	?	No
Transport characteristics	Possible	Possible	?	No
Format capabilities	Yes	Yes	?	No
Volume capabilities	Yes	Yes	?	No
Latency
Per-feature	No	Yes	?	No
# of channels
Channels and/or data slots i.e. high speed data	2 Max	Plenty	?	3 Max
Link stability
Dropout mitigation	Only HFP	No	?	No
Control
Audio processing disablement	Yes	Yes	?	No
Bidirectional media (2 capture, 2 render)	Possible	Yes	?	Possible
Bidirectional audio
Incoming to host:
Post-process reference signal	No	Yes	?	Possible
ANC reference signal	No	No	?	Possible
Recording	Yes	Yes	?	Yes
Security
Stream interception prevention
Wireless: encryption	Yes	N/A	Yes	N/A
Wired: N/A	N/A	Yes	N/A	No
Multi-endpoint
Broadcast	No	No	?	Yes
Aggregation	No	No	?	No
Multi-source
Dynamic source switching	No	No	?	No
Intelligent source ranking	N/A	N/A	?	No
Public barge-in i.e. accept incoming public streams	No	No	No	No
Power modes
Power/perf gradience	No	No	?	N/A
Low power states	Yes	Yes	Yes	N/A
Auto sleep/wake	Yes	Yes	Yes	N/A
Cost
It matters	Yes	Yes	Yes	Yes
Quality of service
Condition-adaptive audio codec	No	No	No	No
Association of non-audio communication
Sensory information	BLE - limited	Possible	?	N/A
Per-endpoint characteristics
Geometry	Possible	Possible	Possible	N/A
Sensitivity	Possible	Possible	Possible	N/A
Non-audio control (to host) without interrupting audio	Yes	Yes	Yes	Possible
Non-audio control (to device) without interrupting audio	Limited	Yes	Yes	Possible
Range
Wireless: 10ft	Yes	Yes	Yes	Yes
Noise
SNR (transport target: 120dB)	Possible	Yes	Yes	Yes
Ease-of-use
Pairing - no hassle	No	N/A	No	Yes
Multiple device pairing	Possible	N/A	No	Yes
Per-user settings	Possible	Possible	?	N/A
Per-device settings	Yes	Yes	?	N/A
Sufficient data to host to enable plug-n-play	N/A	Yes	N/A	Yes

section 6

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select a section:
1. Introduction
2. Workgroup Reports Overview
3. An Exploration of Machine Learning and the use cases where it might provide the most benefit for Audio Synthesis
4. Benchmarking methodology for a multi-voice assistant enabled future
5. Problems and Solutions for Audio in Augmented Reality Headsets
6. A World Without 3.5mm: Transport Features, Guidelines, and Opportunities
7. Pork Rinds: Challenges with the present hearable model
8. Taking the "virtual" out of virtual audio
9. Impact of non-traditional sound: mic used for ultrasonic, etc. Everything is broken!
10. Schedule & Sponsors