1. Speech Communications
ECE 796/896 Chapter 7
Speech Communications

2. Defining Speech Types of speech sounds
Phoneme: The shortest segment of speech, which if changed would change the meaning of the word.
13 vowel sounds, 25 consonants in english
Diphthongs: special phonemes (oy in boy)

3. Depicting Speech
Speech can be shown as, wave forms,spectrum, and sound spectrogram.

5. Criteria for Evaluating Speech
1. Intelligibility
2. Quality
Components of Speech Communication Systems
Speaker, Message,transmission system, noise environment, hearer

6. Speaker Enunciation: Superior speakers: Longer “syllable duration”
Greater intensity
Utilized more of the total time w/ speech sounds
Varied speech more in fundamental frequencies

7. Message Phoneme Confusions:
Certain speech sounds are more easily confused than others.
DVPBGCET, FXSH, KJA,MN noise tends to confuse
MNDGBVZ,TKPFS
Avoid using single letters as codes

8. Message Cont. Word Characteristics Context Features
Intelligibility is better with familiar words
Letters vs. word-spelling letter
Context Features
Vocabulary small as possible
Standard sentence constructions
Avoid short words - word spelling alphabet
Familiarize the receiver with words and sentence structure

9. Transmission System Frequency Distortion Filtering
Amplitude Distortion
Modifications of the time scale
If intelligibility is important (Amp Dis.) can still result in acceptable intelligibility

10. Transmission cont. Effects of filtering on speech
Low and High pass filters
Effects of Amplitude Distortion on speech
Peak clipping

13. Noise Environment
Indices that evaluate the effects of noise on speech intelligibility.
AI: Articulation index
PSIL: Preferred-octave speech interference
PNC: Preferred noise criteria

14. Articulation Index
Articulation index was developed to predict speech intelligibility given a knowledge of the noise environment.
AI is a good predictor of speech intelligibility for normal and hearing impaired with mild-moderate hearing loss.

15. AI Cont. One Technique for computing AI.
1. For each 1/3 octave band, plot their band level of the speech peak reaching the listener’s ear.
2. Plot the steady state noise.
3. Computer the difference in levels between the two.
Noise > speech = 0
Noise +30db > speech = 30
Multiply this by value for each band
Add the values and the sum = AI

17. AI Cont.
An AI = > 75% of 1000 word vocabulary would be understood, while almost 96% of a 256 word would be understood.
AI <.3 poor, acceptable, > .5 good, >.7 excellent

19. PSIL - Preferred Octave Speech Interference Level
PSIL is the numeric average of the noise level in three bands (500,1000,2000Hz).
EX: 70,80,75 --> PSIL = 75
This is not an effective measure when there are noise peaks outside these bands,

20. Speech Interference Level
SIL: an average of decibel level in the bands( , , ).

22. Preferred Noise Criteria
Curves Developed to evaluate noise environment inside office buildings.
Based on the NC curves.

23. Guidelines of Synthesized Speech
1. Voice warnings should be presented in a voice that is qualitatively different from other voices in the environment.
2. There should be no alerting tones.
3. Directing attention to the voice warning.
4. Max. Intelligibility of the message
5. Make the voice as natural as possible.
6. Provide replay mode.
7. If spelling mode is provided, its quality may need to be better than that used for ther rest of the system.
8. Ability to interrupt, important for experienced users.
9. Provide training message.
10. Use sparingly and where it is acceptable.