Wideband Speech Communications: the Good, the Bad, and the Ugly

1. Wideband Speech Communications: the Good, the Bad, and the Ugly Scott Pennock Sr. Hands-Free Standards Specialist QNX Software Systems (Wavemakers)

2. Outline • Introduction • The Good • The Bad • The Ugly • Conclusions

3. Introduction • What is wideband (WB) speech? • Speech has energy from around 50-10000Hz • Traditional narrowband (NB) terminals and networks bandlimit speech down to around 300-3400Hz • WB speech in this presentation refers to a bandwidth of 50-7000Hz • Why is WB speech important to automotive? • More robust to vehicle noise • Reduces driver distraction • Helps enable spatial auditory displays • This presentation will review the benefits, challenges, and unresolved issues with WB speech in an automotive environment

4. The “Good” • Improves task performance • Better speech comprehension • Reduced driver distraction • Improved talker identification • Better speech localization • Other potential task improvements • Preferred by users • Higher quality • Less listening-effort • More comfortable loudness-level • Other factors influencing preference • Task performance benefits alone make a compelling argument for deploying WB speech in the vehicle

5. This “difference spectrogram” was calculated by subtracting the NB from WB spectrogram of someone saying “the juice of lemons makes fine punch”. WB speech provides extra frequency and temporal information

6. Probability of correct response by bandwidth and SNR WB speech increases intelligibility and is more robust to vehicle noise

7. This figure illustrates auditory streaming of speech. Shapes represent phonetic units that have been recognized. Dotted lines show information that would be missing without wideband speech. WB speech improves speech comprehension and reduces driver distraction

8. The “Bad” • Users are more sensitive to WB echo and noise due to perceptual effects • Ear is most sensitive to high frequency region of WB speech • Loudness of echo and noise in new frequency regions will add to loudness in narrowband region • High frequency echo is not masked as effectively by one’s own voice • Acoustic Echo Cancellers (AEC) have a more difficult time removing high frequency echo • Poor excitation signal makes it harder to drive echo canceller to convergence • High frequency distortion is falsely classified as driver’s speech and can prevent AEC from training

9. The challenges presented by WB speech can be addressed • Good electro-acoustic design of vehicle platforms • Careful acoustic design of vehicle cabin • Proper selection, placement, orientation, and mounting of microphones and loudspeakers • High quality signal transport (e.g., optical, differential) • High performance speech enhancement algorithms • AEC • Noise Reduction (NR) • Low-complexity compression for devices with limited resources

10. The “Ugly” • Interoperability issues • WB terminal users will experience inconsistent loudness and quality • NB terminal users will become less satisfied with quality because of exposure to WB speech • Long transition period

11. Users of WB terminals will experience inconsistent loudness and quality • Solution for inconsistent loudness is to use Receive Automatic Gain Control (AGC) based on perceived loudness instead of RMS or peak levels • Differences in quality can be reduced by using BandWidth Extension (BWE) and High Frequency Encoding (HFE) techniques

12. There will be a long transition period • Deployment has already started • Not clear when WB speech will take-off, but automotive is already well positioned • Vehicle Audio Systems are currently wideband capable • WB microphones available and easy to drop-in • Several WB speech coders are already standardized • Even after WB speech takes hold, hybrid WB/NB connections will be around for a long time • NB network equipment and terminals are built to last • Continued use in certain areas

13. Conclusions • WB speech improves task performance • Users prefer WB speech • WB speech is important to automotive • More robust to vehicle noise • Reduces driver distraction • Helps enable spatial auditory displays • WB speech will be a key differentiator for automotive OEMs and service providers

14. Conclusions (continued) • Successful automotive deployment depends on: • Attention to the design of vehicle platforms • High performance speech enhancement algorithms (e.g., AEC, NR, etc.) • Interoperability issues will eventually get worked out • NB network equipment/terminals will be in use in certain areas for a long time