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The Twenty-third Annual Interactive Audio Conference
PROJECT BAR-B-Q 2018
BBQ 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  
  PDF download the PDF
 

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

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

 

next section

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