音声明瞭度 STI

XL2 STIPA Analyzer

教室、会議場、ショッピングセンター、スタジアム、駅、空港、コンサートホールなどの公共の場において、アナウンス放送は人々に十分理解されなければいけません。特に、非常時に明瞭な避難誘導のアナウンスを届けることは重要です。そのため、正確で再現性の高い方法を用いて、このような場所で音声明瞭度を検証することは必須となります。

Speech Transmission Index STIは、放送メッセージの明瞭度を評価する際の最も確立された測定手法です。

特長

  • 音声明瞭度STIの解析
  • 容易な測定手順
  • 標準に準拠したレポート作成

Basics

音声明瞭度は、アナウンス放送システムから既知の信号(STIPAテスト信号)を出力し、各測定位置に到達した際の信号の変質度を測定することで評価します。 The IEC 60268-16 standard for STI defines how any degradation in the signal is measured and the intelligibility result displayed as a single number from 0 (unintelligible) to 1 (excellent intelligibility). Measurement units are STI (Speech Transmission Index) or CIS (Common Intelligibility Scale).


Factors that influence the intelligibility of speech

  • 音圧レベル(大き過ぎない程度の十分な音量が求められる)
  • 周囲騒音レベル(人が大勢いる場所や交通量の多い場所)
  • 残響時間(一定の反響は必要だが、大き過ぎる反響は音声明瞭度を低下させる)

Also, if a Public Address (PA) system is being used for the announcements

  • frequency response of the PA system (e.g. too much bass)
  • SN比(放送設備の性能に関連する)

STIPAテスト信号

The STIPA test signal is a modulated sinusoidal Pink Noise in the octave band range from 125 Hz to 8 kHz. The modulation and range mimics a person’s voice with its varying intensity over time. Nevertheless, the STIPA test signal sounds nothing like a human voice; it is a modulated Pink Noise.

Rooms without Audio Systems

In locations such as classrooms, where no PA system is installed, the STIPA test signal should be reproduced by an appropriate loudspeaker at the position and with the typical sound pressure level of the speaker (the teacher). Requirements for such a loudspeaker are defined in the IEC 60268-16 standard, which states that the typical level of a human talker corresponds to 60 dBA @ 1 m distance.

Furthermore, the ITU-T P.51 standard defines an appropriate loudspeaker to be one where the radiation characteristic corresponds broadly to that of a human mouth.

The Talkbox acoustic signal generator with built-in loudspeaker is designed for this application.
 


Audio Systems with Voice Microphones

In locations where the announcement is picked up by a voice microphone, and then broadcast through a PA system, the STIPA test signal must be replayed acoustically into the microphone. For this purpose, an appropriate loudspeaker is required to present the standardized voice-like acoustic signal, simulating a human talker according to IEC 60268-16, at the correct levels. This setup considers the entire signal path for an accurate speech intelligibility measurement, including all effects of the operator's microphone and environment.

Again, the Talkbox acoustic signal generator + loudspeaker is designed for this application.


Minirator MR-PRO

Audio Systems without Voice Microphones

If the location comprises of a PA system including a hard drive to replay pre-recorded announcements, the STIPA test signal must be injected electronically from an external sound generator. This generator must be able to continuously play the STIPA test signal at selectable line levels.

The MR-PRO audio signal generator is designed for this application.
 


XL2 Sound Level Meter

STI Measurement

For the evaluation of the acoustic STIPA test signal, you need an STI analyzer. It is recommended that this device be hand-held and portable. The reason is that, for the complete STI assessment of a room, you typically have to execute several measurements at different positions, each of them lasting 15 seconds.

After averaging this data, and optionally applying ambient noise correction, it will be convenient for you to check the results immediately. This allows you to implement changes to the acoustics of the room straight away, if necessary, in order to improve the speech intelligibility, and measure again.

The XL2 STIPA Analyzer is designed for this.

STI レポーティングツール

The final task of an STI assessment is to create a measurement report according to one or more of the following standards

  • AS 1670.4
  • CEN/TS 54-32:2015
  • DIN EN 50849:2017
  • IEC 60268-16
  • ISO 7240-19:2007
  • VDE V 0833-4-32:2016
  • VDE 0828-1:2017-11

You could therefore do with a tool that provides such a report, additionally calculating the effect of ambient noise on the STI result.

STI-Messbericht

The STI Reporting Tool provides such a solution.

システム必要条件:
  • PC Windows XP, 7, 8, 10
  • Excel 2010, 2013, 2016(32ビットまたは64ビット)

4 音声明瞭度の測定手順

  1. 1.
    測定場所に人が大勢いる場合は、XL2アナライザで騒音を記録します。
    XL2 STIPA background measurement
  2. 2.
    測定場所に人がいない状態(例えば夜間)、TalkBoxを話者が使用するマイクロホンの前に設置します。
    TalkBox with announcement microphone
  3. 3.
    XL2のスタートボタンを押してSTIを測定します。
    XL2 STIPA measurement
  4. 4.
    レポートを作成します。
    STIPA Report with your logo

音声明瞭度測定ガイドのダウンロードはこちら

Optimize Speech Intelligibility

最も良好な音声明瞭度は、70~80dBSPLで得られます。音圧レベ ルが高すぎると聴覚保護作用により明瞭度が低下します。If you’ve measured, for example, a perfect intelligibility of 1.00 STI in a room with a speaker level of 70 dBSPL, then the maximum intelligibility in the room would reduce down to 0.90 STI if the announcement level were to increase to 90 dBSPL.

音声明瞭度測定を解説したウェビナー動画

本ウェビナーでは、音声明瞭度(STIPA)の測定方法とワークフローを解説し、レポート作成方法を紹介します。

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