Sample Sounds and How They Relate to the Proposed Rulemaking

These sounds files are examples of sounds that could be proposed for use as alerting sounds. Some of these sounds would meet the proposed specifications; some would not. With the exception of the first three sounds, all sounds are based on an ICE vehicle sound. Other sounds that are not based on ICE vehicle sounds could also be proposed. It is expected that all alert sounds meeting the proposed specifications will be recognizable as a vehicle in operation due to requirements in the proposal for increasing sound level and pitch shifting with vehicle speed, as well as the innate characteristics associated with a moving vehicle.

All of the sounds included here are presented monaurally, that is, when played through headphones, the sound presented to each ear is the same; therefore pass-by events will not be perceived as, for example, moving from the left to right as one will experience in the field. With the exception of sounds 1 and 2, the sounds do not include tire noise; however at 10 km/h, tire noise is not a major contributor. Finally, the relative loudness of low frequency components to high frequency components will depend on individual playback equipment and settings. When the sound files are played at high levels, the low frequency sound will be greater relative to the high frequency sound than when the sound files are played at low levels. If headphones or speakers are not “flat”, they will accentuate particular regions of the sound. It is recommended that these sounds be listened to through high quality “monitor type” headphones at moderate level.

In order to provide context, alert sounds are combined with an ambient (background sound). The same ambient is used for all alert sounds with the exception of sounds 11 through 14, which focus on the tone-to-noise ratio of the alert sound itself. The ambient consists of pink noise filtered such that the spectral shape conforms to the average of several typical ambient conditions as described in White Paper on External Warning Sounds for Electric Cars: Recommendations and Guidelines. DELTA SenseLab, Pedersen, Torben et al (2011). The overall A-weighted level of the ambient was set to 55 dB(A), which is the level that was used to determine minimum one-third octave band levels for the alert sounds. Real ambient conditions generally contain some slow variations in level, which are not present in the simulated ambient, however, this ambient provides a consistent, documentable condition that has the same masking effect at all times.

With the exception of Sounds 1, 2, and 3, all sounds are based on an idling ICE vehicle that is modified. Broadband spectra are adjusted; tones are added, overall levels are adjusted to account for the vehicle approaching a pedestrian, and Doppler shifts are added. Each sound contains six seconds of approach. At time t = 6 seconds, the sound is representative of the sound as the vehicle arrives at a pedestrian’s location. Sounds 3 through 14 also include 6 seconds of departure.


Reference Sounds

These are sample sounds of what a typical internal combustion engine vehicle should sound like through speakers on your computer. This will allow you to compare them with the sample sounds of the proposed rulemaking.

  • Sound (A) sound is a monaural recording of an existing ICE economy vehicle (4-cylinder) traveling at a constant speed of 10 km/h, approaching a pedestrian.
  • Sound (B) sound is a monaural recording of an existing ICE SUV (V6) traveling at a constant speed of 10 km/h, approaching a pedestrian.

Sound File Descriptions

  • Sound One (1) sound is a monaural recording of an existing electric vehicle’s alert sound traveling at a constant speed of 10 km/h, approaching a pedestrian. It does not meet the proposed requirements for detection, only exceeding the minimum level in the 2500 Hz one-third octave band. The lowest tone that could be clearly identified was at 2550 Hz, this would not meet the proposed specification for tonal component for recognition since it is above 400 Hz.
  • Sound Two (2) sound is a monaural recording of an existing electric vehicle’s alert sound traveling at a constant speed of 10 km/h, approaching a pedestrian. The level of each one-third octave band has been adjusted so that it just meets the proposed detection requirements in all one-third octave bands. In so doing, all specified one-third octave bands are very close to the proposed minimum proposed detection requirements. The lowest tone that could be clearly identified was at 1100 Hz, this would not meet the proposed tonal requirements since it is above 400 Hz.
  • Sound Three (3) sound is based on low levels of broadband noise and strong tonal components that have been slightly modulated in pitch and amplitude to produce a rich tonal sound. This sound was optimized to just meet the proposed detection requirements in all specified one-third octave bands.
  • Sound Four (4) sound is a synthesized 10 km/h, constant speed, pass-by sound based on the resampling of an ICE vehicle at idle. The sound was processed so that it included level changes and Doppler due to the approach towards the pedestrian. A tone was added to the signal at 290 Hz to meet the proposed tonal requirements. This sound was optimized to just meet the proposed detection requirements in all specified one-third octave bands.
  • Sound Five (5) sound is a synthesized 10 km/h, constant speed, pass-by sound based on an ICE vehicle at idle. The sound is similar to four, except that rather than resampling an idle sound, filtered noise was used to generate the sound. The sound was processed so that it included level changes and Doppler due to the approach towards the pedestrian. A tone was added to the signal at 290 Hz to meet the proposed tonal requirements. This sound was optimized to just meet the proposed detection requirements in all specified one-third octave bands.
  • Sound Six (6) sound is a synthesized 10 km/h, constant speed, pass-by sound based on an ICE vehicle at idle. The sound is similar to five, except that the sound has been adjusted so that its level is 10 dB greater than the minimum proposed requirements.
  • Sound Seven (7) sound is a synthesized 10 km/h, constant speed, pass-by sound based on an ICE vehicle at idle. The sound is similar to five, except that the sound has been adjusted so that its level is 10 dB less than the minimum proposed requirements.
  • Sound Eight (8) sound is a synthesized 10 km/h, constant speed, pass-by sound that is generated by passing broad band noise through a single one-third octave band filter centered at 315 Hz. The sound was processed so that it included level changes and Doppler due to the approach towards the pedestrian. The sound meets the minimum proposed requirement in the 315 Hz band only and does not contain any tones.
  • Sound Nine (9) sound is a synthesized 10 km/h, constant speed, pass-by sound that is generated by passing broad band noise through a single one-third octave band filter centered at 5000 Hz. The sound was processed so that it included level changes and Doppler due to the approach towards the pedestrian. The sound meets the minimum proposed requirement in the 5000 Hz band only and does not contain any tones.
  • Sound Ten (10) sound is a synthesized 10 km/h, constant speed, pass-by sound that is generated by adding two 45 dB(A) pure tones, one at 315 Hz and one at 2500 Hz. The sound was processed so that it included level changes and Doppler due to the approach towards the pedestrian. The combination of these two tones provide an overall level of 48 dB(A). This sound does not meet the proposed requirements.
  • Sound Eleven (11) sound is a synthesized 10 km/h, constant speed, pass-by sound that is generated from a base, broad band noise that has been optimized to meet the minimum proposed requirement. Added to this is a pure tone at 315 Hz with a level sufficient to produce a Tone-to-Noise Ratio (TNR) of 6 dB. Thus this sound just meets the proposed requirements for TNR. Note, that because the tone is added to a sound that already meets the minimum proposed detection requirements, this sound exceeds the minimum requirements in the 315 Hz one-third octave band by 7 dB.
  • Sound Twelve (12) sound, Sound Thirteen (13) sound, and Sound Fourteen (14) sound are similar to Sound Eleven (11) except that the TNR is increased to 8, 14, and 20 dB respectively (giving total levels in the 315 Hz band of 9, 15, and 22 dB(A)). Comparing these sounds allows one to appreciate the effect of increasing TNR.