forked from w3c/csswg-drafts
-
Notifications
You must be signed in to change notification settings - Fork 0
Expand file tree
/
Copy pathOverview.html
More file actions
executable file
·4050 lines (3064 loc) · 146 KB
/
Overview.html
File metadata and controls
executable file
·4050 lines (3064 loc) · 146 KB
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<html lang=en>
<head>
<title>CSS Speech Module</title>
<meta content="text/html; charset=utf-8" http-equiv=Content-Type>
<link href="../default.css" rel=stylesheet type="text/css">
<style type="text/css">
p
{
padding-bottom : 1em;
}
p + p
{
text-indent : 0;
}
*:target
{
border : 1px dashed #66CC66;
}</style>
<!--
.prod
{
font-family : inherit;
font-size : inherit
}
pre.prod
{
white-space : pre-wrap;
margin : 1em 0 1em 2em
}
code
{
font-size : inherit;
}
#box-shadow-samples td
{
background : white;
color : black;
}
caption
{
text-align : left;
font-weight : bold
}
.note
{
font-style : italic
}
.issue
{
color : maroon;
font-style : italic
}
div.example pre
{
color : green;
margin-left : 2em
}
dl
{
margin-left : 2em
}
caption dfn
{
font-size : 120%
}
-->
<link href="http://www.w3.org/StyleSheets/TR/W3C-ED" rel=stylesheet
type="text/css">
<body>
<div class=head> <!--begin-logo-->
<p><a href="http://www.w3.org/"><img alt=W3C height=48
src="http://www.w3.org/Icons/w3c_home" width=72></a> <!--end-logo-->
<h1 id=top>CSS Speech Module</h1>
<h2 class="no-num no-toc" id=longstatus-date>Editor's Draft 20 March 2012</h2>
<dl id=versions>
<dt>This version:
<dd>
<!--<a href="http://www.w3.org/TR/2012/WD-css3-speech-20120320/">http://www.w3.org/TR/2012/ED-css3-speech-20120320/</a>-->
<a
href="http://dev.w3.org/csswg/css3-speech">http://dev.w3.org/csswg/css3-speech</a>
<dt>Latest version:
<dd> <a
href="http://www.w3.org/TR/css3-speech/">http://www.w3.org/TR/css3-speech/</a>
<dt>Previous versions:
<dd> <a
href="http://www.w3.org/TR/2011/WD-css3-speech-20110818/">http://www.w3.org/TR/2011/WD-css3-speech-20110818/</a>
<dt>Feedback:
<dd><a href="mailto:www-style@w3.org?subject=%5Bcss-speech%5D%20feedback">www-style@w3.org</a>
with subject line “<kbd>[css-speech] <var>… message topic …</var></kbd>”
(<a rel="discussion" href="http://lists.w3.org/Archives/Public/www-style/">archives</a>)
</dl>
<dl id=editors-list>
<dt>Editor:
<dd><a href="mailto:dweck@daisy.org">Daniel Weck</a> (<a
href="http://www.daisy.org">DAISY Consortium</a>)
<dt>Former editors:
<dd><a href="mailto:dsr@w3.org">Dave Raggett</a> (<a
href="http://www.w3.org/">W3C</a>/<a
href="http://www.canon.com/">Canon</a>)
<dd><a href="mailto:daniel@glazman.org">Daniel Glazman</a> (<a
href="http://www.disruptive-innovations.com/">Disruptive
Innovations</a>)
<dd><a href="mailto:csant@opera.com">Claudio Santambrogio</a> (<a
href="http://www.opera.com/">Opera Software</a>)
</dl>
<!--begin-copyright-->
<p class=copyright><a
href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright"
rel=license>Copyright</a> © 2012 <a href="http://www.w3.org/"><abbr
title="World Wide Web Consortium">W3C</abbr></a><sup>®</sup> (<a
href="http://www.csail.mit.edu/"><abbr
title="Massachusetts Institute of Technology">MIT</abbr></a>, <a
href="http://www.ercim.eu/"><abbr
title="European Research Consortium for Informatics and Mathematics">ERCIM</abbr></a>,
<a href="http://www.keio.ac.jp/">Keio</a>), All Rights Reserved. W3C <a
href="http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>,
<a
href="http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a>
and <a
href="http://www.w3.org/Consortium/Legal/copyright-documents">document
use</a> rules apply.</p>
<!--end-copyright-->
<hr title="Separator for header">
</div>
<h2 class="no-num no-toc" id=abstract>Abstract</h2>
<p>CSS (Cascading Style Sheets) is a language that describes the rendering
of markup documents (e.g. HTML, XML) on various supports, such as screen,
paper, speech, etc. The Speech module defines aural CSS properties that
enable authors to declaratively control the rendering of documents via
speech synthesis, and using optional audio cues. Note that this standard
was developed in cooperation with the <a
href="http://www.w3.org/Voice/">Voice Browser Activity</a>.
<h2 class="no-num no-toc" id=status>Status of this document</h2>
<!--begin-status-->
<p>This is a public copy of the editors' draft. It is provided for
discussion only and may change at any moment. Its publication here does
not imply endorsement of its contents by W3C. Don't cite this document
other than as work in progress.
<p>The (<a
href="http://lists.w3.org/Archives/Public/www-style/">archived</a>) public
mailing list <a
href="mailto:www-style@w3.org?Subject=%5Bcss3-speech%5D%20PUT%20SUBJECT%20HERE">
www-style@w3.org</a> (see <a
href="http://www.w3.org/Mail/Request">instructions</a>) is preferred for
discussion of this specification. When sending e-mail, please put the text
“css3-speech” in the subject, preferably like this:
“[<!---->css3-speech<!---->] <em>…summary of
comment…</em>”
<p>This document was produced by the <a href="/Style/CSS/members">CSS
Working Group</a> (part of the <a href="/Style/">Style Activity</a>).
<p>This document was produced by a group operating under the <a
href="/Consortium/Patent-Policy-20040205/">5 February 2004 W3C Patent
Policy</a>. W3C maintains a <a href="/2004/01/pp-impl/32061/status"
rel=disclosure>public list of any patent disclosures</a> made in
connection with the deliverables of the group; that page also includes
instructions for disclosing a patent. An individual who has actual
knowledge of a patent which the individual believes contains <a
href="/Consortium/Patent-Policy-20040205/#def-essential">Essential
Claim(s)</a> must disclose the information in accordance with <a
href="/Consortium/Patent-Policy-20040205/#sec-Disclosure">section 6 of the
W3C Patent Policy</a>.</p>
<!--end-status-->
<!-- <h3 class="no-num no-toc" id="maturity">Maturity Level</h3> -->
<p> This document is based on the <a
href="http://www.w3.org/TR/2011/WD-css3-speech-20110818/">Last Call
Working Draft (18 August 2011)</a> and includes changes that reflect the
outcome of the <a
href="http://wiki.csswg.org/spec/css3-speech">disposition of comments</a>.
<p>Before the specification can progress to <a
href="http://www.w3.org/2005/10/Process-20051014/tr#cfr">Proposed
Recommendation,</a> the <a href="#exit">CR exit criteria</a> must be met.
The specification will not become Proposed Recommendation before 20
September 2012. A test suite and an implementation report will be made
during the Candidate Recommendation period.
<p id=at-risk>The following features are at-risk and may be dropped at the
end of the Candidate Recommendation period if there has not been enough
interest from implementers: ‘<a href="#voice-balance"><code
class=property>voice-balance</code></a>’, ‘<a
href="#voice-duration"><code
class=property>voice-duration</code></a>’, ‘<a
href="#voice-pitch"><code class=property>voice-pitch</code></a>’,
‘<a href="#voice-range"><code
class=property>voice-range</code></a>’, and ‘<a
href="#voice-stress"><code class=property>voice-stress</code></a>’.
<h2 class="no-num no-toc" id=contents>Table of contents</h2>
<!--begin-toc-->
<ul class=toc>
<li><a href="#intro"><span class=secno>1. </span>Introduction, design
goals</a>
<li><a href="#background"><span class=secno>2. </span>Background
information, CSS 2.1</a>
<li><a href="#ssml-rel"><span class=secno>3. </span>Relationship with
SSML</a>
<li><a href="#css-values"><span class=secno>4. </span>CSS values</a>
<li><a href="#example"><span class=secno>5. </span>Example</a>
<li><a href="#aural-model"><span class=secno>6. </span>The aural
formatting model</a>
<li><a href="#mixing-props"><span class=secno>7. </span>Mixing
properties</a>
<ul class=toc>
<li><a href="#mixing-props-voice-volume"><span class=secno>7.1.
</span>The ‘<code class=property>voice-volume</code>’
property</a>
<li><a href="#mixing-props-voice-balance"><span class=secno>7.2.
</span>The ‘<code class=property>voice-balance</code>’
property</a>
</ul>
<li><a href="#speaking-props"><span class=secno>8. </span>Speaking
properties</a>
<ul class=toc>
<li><a href="#speaking-props-speak"><span class=secno>8.1. </span>The
‘<code class=property>speak</code>’ property</a>
<li><a href="#speaking-props-speak-as"><span class=secno>8.2. </span>The
‘<code class=property>speak-as</code>’ property</a>
</ul>
<li><a href="#pause-props"><span class=secno>9. </span>Pause properties
</a>
<ul class=toc>
<li><a href="#pause-props-pause-before-after"><span class=secno>9.1.
</span>The ‘<code class=property>pause-before</code>’ and
‘<code class=property>pause-after</code>’ properties</a>
<li><a href="#pause-props-pause"><span class=secno>9.2. </span>The
‘<code class=property>pause</code>’ shorthand property</a>
<li><a href="#collapsed-pauses"><span class=secno>9.3. </span>Collapsing
pauses</a>
</ul>
<li><a href="#rest-props"><span class=secno>10. </span>Rest properties</a>
<ul class=toc>
<li><a href="#rest-props-rest-before-after"><span class=secno>10.1.
</span>The ‘<code class=property>rest-before</code>’ and
‘<code class=property>rest-after</code>’ properties</a>
<li><a href="#rest-props-rest"><span class=secno>10.2. </span>The
‘<code class=property>rest</code>’ shorthand property</a>
</ul>
<li><a href="#cue-props"><span class=secno>11. </span>Cue properties</a>
<ul class=toc>
<li><a href="#cue-props-cue-before-after"><span class=secno>11.1.
</span>The ‘<code class=property>cue-before</code>’ and
‘<code class=property>cue-after</code>’ properties</a>
<li><a href="#cue-props-volume"><span class=secno>11.2. </span>Relation
between audio cues and speech synthesis volume levels</a>
<li><a href="#cue-props-cue"><span class=secno>11.3. </span>The
‘<code class=property>cue</code>’ shorthand property</a>
</ul>
<li><a href="#voice-char-props"><span class=secno>12. </span>Voice
characteristic properties</a>
<ul class=toc>
<li><a href="#voice-props-voice-family"><span class=secno>12.1.
</span>The ‘<code class=property>voice-family</code>’
property</a>
<li><a href="#voice-props-voice-rate"><span class=secno>12.2. </span>The
‘<code class=property>voice-rate</code>’ property</a>
<li><a href="#voice-props-voice-pitch"><span class=secno>12.3.
</span>The ‘<code class=property>voice-pitch</code>’
property</a>
<li><a href="#voice-props-voice-range"><span class=secno>12.4.
</span>The ‘<code class=property>voice-range</code>’
property</a>
<li><a href="#voice-props-voice-stress"><span class=secno>12.5.
</span>The ‘<code class=property>voice-stress</code>’
property</a>
</ul>
<li><a href="#duration-props"><span class=secno>13. </span>Voice duration
property</a>
<ul class=toc>
<li><a href="#mixing-props-voice-duration"><span class=secno>13.1.
</span>The ‘<code class=property>voice-duration</code>’
property</a>
</ul>
<li><a href="#lists"><span class=secno>14. </span>List items and counters
styles</a>
<li><a href="#content"><span class=secno>15. </span>Inserted and replaced
content</a>
<li><a href="#pronunciation"><span class=secno>16. </span> Pronunciation,
phonemes </a>
<li class=no-num><a href="#property-index">Appendix A — Property
index</a>
<li class=no-num><a href="#index">Appendix B — Index</a>
<li class=no-num><a href="#definitions">Appendix C — Definitions</a>
<ul class=toc>
<li class=no-num><a href="#glossary">Glossary</a>
<li class=no-num><a href="#conformance">Conformance</a>
<li class=no-num><a href="#exit">CR exit criteria</a>
</ul>
<li class=no-num><a href="#ack">Appendix D — Acknowledgements</a>
<li class=no-num><a href="#changes">Appendix E — Changes from
previous draft</a>
<li class=no-num><a href="#references&q
2B9
uot;>Appendix F — References</a>
<ul class=toc>
<li class=no-num><a href="#normative-references">Normative
references</a>
<li class=no-num><a href="#other-references">Other references</a>
</ul>
</ul>
<!--end-toc-->
<h2 id=intro><span class=secno>1. </span>Introduction, design goals</h2>
<p class=note>Note that this section is informative.
<p>The aural presentation of information is commonly used by people who are
blind, visually-impaired or otherwise print-disabled. For instance,
"screen readers" allow users to interact with visual interfaces that would
otherwise be inaccessible to them. There are also circumstances in which
<em>listening</em> to content (as opposed to <em>reading</em>) is
preferred, or sometimes even required, irrespective of a person's physical
ability to access information. For instance: playing an e-book whilst
driving a vehicle, learning how to manipulate industrial and medical
devices, interacting with home entertainment systems, teaching young
children how to read.
<p> The CSS properties defined in the Speech module enable authors to
declaratively control the presentation of a document in the aural
dimension. The aural rendering of a document combines speech synthesis
(also known as "TTS", the acronym for "Text to Speech") and auditory icons
(which are referred-to as "audio cues" in this specification). The CSS
Speech properties provide the ability to control speech pitch and rate,
sound levels, TTS voices, etc. These stylesheet properties can be used
together with visual properties (mixed media), or as a complete aural
alternative to a visual presentation.
<h2 id=background><span class=secno>2. </span>Background information, CSS
2.1</h2>
<p class=note>Note that this section is informative.
<p> The CSS Speech module is a re-work of the informative CSS2.1 Aural
appendix, within which the "aural" media type was described, but also
deprecated (in favor of the "speech" media type). Although the <a
href="#CSS21" rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a> specification
reserves the "speech" media type, it doesn't actually define the
corresponding properties. The Speech module describes the CSS properties
that apply to the "speech" media type, and defines a new "box" model
specifically for the aural dimension.
<p> Content creators can conditionally include CSS properties dedicated to
user agents with text to speech synthesis capabilities, by specifying the
"speech" media type via the <code>media</code> attribute of the
<code>link</code> element, or with the <code>@media</code> at-rule, or
within an <code>@import</code> statement. When styles are authored within
the scope of such conditional statements, they are ignored by user agents
that do not support the Speech module.
<h2 id=ssml-rel><span class=secno>3. </span>Relationship with SSML</h2>
<p class=note>Note that this section is informative.
<p>Some of the features in this specification are conceptually similar to
functionality described in the Speech Synthesis Markup Language (SSML)
Version 1.1 <a href="#SSML" rel=biblioentry>[SSML]<!--{{!SSML}}--></a>.
However, the specificities of the CSS model mean that compatibility with
SSML in terms of syntax and/or semantics is only partially achievable. The
definition of each property in the Speech module includes informative
statements, wherever necessary, to clarify their relationship with similar
functionality from SSML.
<h2 id=css-values><span class=secno>4. </span>CSS values</h2>
<p>This specification follows the <a
href="http://www.w3.org/TR/CSS21/about.html#property-defs">CSS property
definition conventions</a> from <a href="#CSS21"
rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>. Value types not defined in
this specification are defined in CSS Value and Units Level 3 <a
href="#CSS3VAL" rel=biblioentry>[CSS3VAL]<!--{{!CSS3VAL}}--></a>.
<p>In addition to the property-specific values listed in their definitions,
all properties defined in this specification also accept the <a
href="http://www.w3.org/TR/CSS21/cascade.html#value-def-inherit">inherit</a>
keyword as their property value. For readability it has not been repeated
explicitly.
<h2 id=example><span class=secno>5. </span>Example</h2>
<div class=example>
<p>This example shows how authors can tell the speech synthesizer to speak
HTML headings with a voice called "paul", using "moderate" emphasis
(which is more than normal) and how to insert an audio cue (pre-recorded
audio clip located at the given URL) before the start of TTS rendering
for each heading. In a stereo-capable sound system, paragraphs marked
with the CSS class "heidi" are rendered on the left audio channel (and
with a female voice, etc.), whilst the class "peter" corresponds to the
right channel (and to a male voice, etc.). The volume level of text spans
marked with the class "special" is lower than normal, and a prosodic
boundary is created by introducing a strong pause after it is spoken
(note how the <code>span</code> inherits the voice-family from its parent
paragraph).</p>
<pre>
h1, h2, h3, h4, h5, h6
{
voice-family: paul;
voice-stress: moderate;
cue-before: url(../audio/ping.wav);
voice-volume: medium 6dB;
}
p.heidi
{
voice-family: female;
voice-balance: left;
voice-pitch: high;
voice-volume: -6dB;
}
p.peter
{
voice-family: male;
voice-balance: right;
voice-rate: fast;
}
span.special
{
voice-volume: soft;
pause-after: strong;
}
...
<h1>I am Paul, and I speak headings.</h1>
<p class="heidi">Hello, I am Heidi.</p>
<p class="peter">
<span class="special">Can you hear me ?</span>
I am Peter.
</p></pre>
</div>
<h2 id=aural-model><span class=secno>6. </span>The aural formatting model</h2>
<p>The CSS formatting model for aural media is based on a sequence of
sounds and silences that occur within a nested context similar to the <a
href="#box-model-def">visual box model</a>, which we name the <dfn
id=aural-box-model>aural "box" model</dfn>. The aural "canvas" consists of
a two-channel (stereo) space and of a temporal dimension, within which
synthetic speech and audio cues coexist. The selected element is
surrounded by ‘<a href="#rest"><code
class=property>rest</code></a>’, ‘<a href="#cue"><code
class=property>cue</code></a>’ and ‘<a href="#pause"><code
class=property>pause</code></a>’ properties (from the innermost to
the outermost position). These can be seen as aural equivalents to
‘<code class=property>padding</code>’, ‘<code
class=property>border</code>’ and ‘<code
class=property>margin</code>’, respectively. When used, the
‘<code class=css>:before</code>’ and ‘<code
class=css>:after</code>’ pseudo-elements <a href="#CSS21"
rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a> get inserted between the
element's contents and the ‘<a href="#rest"><code
class=property>rest</code></a>’.
<p> The following diagram illustrates the equivalence between properties of
the visual and aural box models, applied to the selected <element>:
<p> <img
alt="The aural 'box' model, illustrated by a diagram: the selected element is positioned in the center, on its left side are (from innermost to outermost) rest-before, cue-before, pause-before, on its right side are (from innermost to outermost) rest-after, cue-after, pause-after, where rest is conceptually similar to padding, cue is similar to border, pause is similar to margin."
id=aural-box src=aural-box.png
title="The aural 'box' model, illustrated by a diagram: the selected element is positioned in the center, on its left side are (from innermost to outermost) rest-before, cue-before, pause-before, on its right side are (from innermost to outermost) rest-after, cue-after, pause-after, where rest is conceptually similar to padding, cue is similar to border, pause is similar to margin.">
<h2 id=mixing-props><span class=secno>7. </span>Mixing properties</h2>
<h3 id=mixing-props-voice-volume><span class=secno>7.1. </span>The
‘<a href="#voice-volume"><code
class=property>voice-volume</code></a>’ property</h3>
<table class=propdef summary="name: syntax">
<tbody>
<tr>
<td>Name:
<td> <dfn id=voice-volume>voice-volume</dfn>
<tr>
<td> <em>Value:</em>
<td>silent | [[x-soft | soft | medium | loud | x-loud] ||
<decibel>]
<tr>
<td> <em>Initial:</em>
<td>medium
<tr>
<td> <em>Applies to:</em>
<td>all elements
<tr>
<td> <em>Inherited:</em>
<td>yes
<tr>
<td> <em>Percentages:</em>
<td>N/A
<tr>
<td> <em>Media:</em>
<td>speech
<tr>
<td> <em>Computed value:</em>
<td>‘<code class=property>silent</code>’, or a keyword value
and optionally also a decibel offset (if not zero)
</table>
<p>The ‘<a href="#voice-volume"><code
class=property>voice-volume</code></a>’ property allows authors to
control the amplitude of the audio waveform generated by the speech
synthesiser, and is also used to adjust the relative volume level of <a
href="#cue-props">audio cues</a> within the <a href="#aural-model">aural
box model</a> of the selected element.
<p class=note> Note that although the functionality provided by this
property is similar to the <a
href="http://www.w3.org/TR/speech-synthesis11/#edef_prosody"><code>volume</code>
attribute of the <code>prosody</code> element</a> from the SSML markup
language <a href="#SSML" rel=biblioentry>[SSML]<!--{{!SSML}}--></a>, there
are notable discrepancies. For example, CSS Speech volume keywords and
decibels units are not mutually-exclusive, due to how values are inherited
and combined for selected elements.
<dl><!-- dt>
<strong>normal</strong>
</dt>
<dd>
<p> Corresponds to +0.0dB, which means that there is no modification of volume level. This
value overrides the inherited value.</p>
</dd -->
<dt> <strong>silent</strong>
<dd>
<p> Specifies that no sound is generated (the text is read "silently").</p>
<p class=note> Note that this has the same effect as using negative
infinity decibels. Also note that there is a difference between an
element whose ‘<a href="#voice-volume"><code
class=property>voice-volume</code></a>’ property has a value of
‘<code class=property>silent</code>’, and an element whose
‘<a href="#speak"><code class=property>speak</code></a>’
property has the value ‘<code class=property>none</code>’.
With the former, the selected element takes up the same time as if it
was spoken, including any pause before and after the element, but no
sound is generated (descendants within the <a href="#aural-model">aural
box model</a> of the selected element can override the ‘<a
href="#voice-volume"><code class=property>voice-volume</code></a>’
value, and may therefore generate audio output). With the latter, the
selected element is not rendered in the aural dimension and no time is
allocated for playback (descendants within the <a
href="#aural-model">aural box model</a> of the selected element can
override the ‘<a href="#speak"><code
class=property>speak</code></a>’ value, and may therefore generate
audio output).</p>
<dt><strong>x-soft</strong>, <strong>soft</strong>,
<strong>medium</strong>, <strong>loud</strong>, <strong>x-loud</strong>
<dd>
<p>This sequence of keywords corresponds to monotonically non-decreasing
volume levels, mapped to implementation-dependent values that meet the
listener's requirements with regards to perceived loudness. These audio
levels are typically provided via a preference mechanism that allow
users to calibrate sound options according to their auditory
environment. The keyword ‘<code
class=property>x-soft</code>’ maps to the user's <em>minimum
audible</em> volume level, ‘<code
class=property>x-loud</code>’ maps to the user's <em>maximum
tolerable</em> volume level, ‘<code
class=property>medium</code>’ maps to the user's
<em>preferred</em> volume level, ‘<code
class=property>soft</code>’ and ‘<code
class=property>loud</code>’ map to intermediary values.</p>
<dt> <strong><decibel></strong>
<dd>
<p>A <a href="#number-def">number</a> immediately followed by "dB"
(decibel unit). This represents a change (positive or negative) relative
to the given keyword value (see enumeration above), or to the default
value for the root element, or otherwise to the inherited volume level
(which may itself be a combination of a keyword value and of a decibel
offset, in which case the decibel values are combined additively). When
the inherited volume level is ‘<code
class=property>silent</code>’, this ‘<a
href="#voice-volume"><code class=property>voice-volume</code></a>’
resolves to ‘<code class=property>silent</code>’ too,
regardless of the specified <decibel> value. Decibels represent
the ratio of the squares of the new signal amplitude (a1) and the
current amplitude (a0), as per the following logarithmic equation:
volume(dB) = 20 log10 (a1 / a0)</p>
<p class=note> Note that -6.0dB is approximately half the amplitude of
the audio signal, and +6.0dB is approximately twice the amplitude.</p>
</dl>
<p class=note>Note that perceived loudness depends on various factors, such
as the listening environment, user preferences or physical abilities. The
effective volume variation between ‘<code
class=property>x-soft</code>’ and ‘<code
class=property>x-loud</code>’ represents the dynamic range (in terms
of loudness) of the audio output. Typically, this range would be
compressed in a noisy context, i.e. the perceived loudness corresponding
to ‘<code class=property>x-soft</code>’ would effectively be
closer to ‘<code class=property>x-loud</code>’ than it would
be in a quiet environment. There may also be situations where both
‘<code class=property>x-soft</code>’ and ‘<code
class=property>x-loud</code>’ would map to low volume levels, such
as in listening environments requiring discretion (e.g. library,
night-reading).
<h3 id=mixing-props-voice-balance><span class=secno>7.2. </span>The
‘<a href="#voice-balance"><code
class=property>voice-balance</code></a>’ property</h3>
<table class=propdef summary="name: syntax">
<tbody>
<tr>
<td>Name:
<td> <dfn id=voice-balance>voice-balance</dfn>
<tr>
<td> <em>Value:</em>
<td><number> | left | center | right | leftwards | rightwards
<tr>
<td> <em>Initial:</em>
<td>center
<tr>
<td> <em>Applies to:</em>
<td>all elements
<tr>
<td> <em>Inherited:</em>
<td>yes
<tr>
<td> <em>Percentages:</em>
<td>N/A
<tr>
<td> <em>Media:</em>
<td>speech
<tr>
<td> <em>Computed value:</em>
<td>the specified
8DCB
value resolved to a <number> between
‘<code class=css>-100</code>’ and ‘<code
class=css>100</code>’ (inclusive)
</table>
<p> The ‘<a href="#voice-balance"><code
class=property>voice-balance</code></a>’ property controls the
spatial distribution of audio output across a lateral sound stage: one
extremity is on the left, the other extremity is on the right hand side,
relative to the listener's position. Authors can specify intermediary
steps between left and right extremities, to represent the audio
separation along the resulting left-right axis.
<p class=note> Note that the functionality provided by this property has no
match in the SSML markup language <a href="#SSML"
rel=biblioentry>[SSML]<!--{{!SSML}}--></a>.
<dl>
<dt> <strong><number></strong>
<dd>
<p>A <a href="#number-def">number</a> between ‘<code
class=css>-100</code>’ and ‘<code
class=css>100</code>’ (inclusive). Values smaller than
‘<code class=css>-100</code>’ are clamped to ‘<code
class=css>-100</code>’. Values greater than ‘<code
class=css>100</code>’ are clamped to ‘<code
class=css>100</code>’. The value ‘<code
class=css>-100</code>’ represents the left side, and the value
‘<code class=css>100</code>’ represents the right side. The
value ‘<code class=css>0</code>’ represents the center point
whereby there is no discernible audio separation between left and right
sides (in a stereo sound system, this corresponds to equal distribution
of audio signals between left and right speakers).</p>
<dt> <strong>left</strong>
<dd>
<p>Same as ‘<code class=css>-100</code>’.</p>
<dt> <strong>center</strong>
<dd>
<p>Same as ‘<code class=css>0</code>’.</p>
<dt> <strong>right</strong>
<dd>
<p>Same as ‘<code class=css>100</code>’.</p>
<dt> <strong>leftwards</strong>
<dd>
<p>Moves the sound to the left, by subtracting 20 from the inherited
‘<a href="#voice-balance"><code
class=property>voice-balance</code></a>’ value, and by clamping
the resulting number to ‘<code class=css>-100</code>’.</p>
<dt> <strong>rightwards</strong>
<dd>
<p>Moves the sound to the right, by adding 20 to the inherited ‘<a
href="#voice-balance"><code
class=property>voice-balance</code></a>’ value, and by clamping
the resulting number to ‘<code class=css>100</code>’.</p>
</dl>
<p> user agents may be connected to different kinds of sound systems,
featuring varying audio mixing capabilities. The expected behavior for
mono, stereo, and surround sound systems is defined as follows:
<ul>
<li> When user agents produce audio via a mono-aural sound system (i.e.
single-speaker setup), the ‘<a href="#voice-balance"><code
class=property>voice-balance</code></a>’ property has no effect.
<li> When user agents produce audio through a stereo sound system (e.g.
two speakers, a pair of headphones), the left-right distribution of audio
signals can precisely match the authored values for the ‘<a
href="#voice-balance"><code
class=property>voice-balance</code></a>’ property.
<li> When user agents are capable of mixing audio signals through more
than 2 channels (e.g. 5-speakers surround sound system, including a
dedicated center channel), the physical distribution of audio signals
resulting from the application of the ‘<a
href="#voice-balance"><code
class=property>voice-balance</code></a>’ property should be
performed so that the listener perceives sound as if it was coming from a
basic stereo layout. For example, the center channel as well as the
left/right speakers may be used altogether in order to emulate the
behavior of the ‘<code class=property>center</code>’ value.
</ul>
<p> Future revisions of the CSS Speech module may include support for
three-dimensional audio, which would effectively enable authors to specify
"azimuth" and "elevation" values. In the future, content authored using
the current specification may therefore be consumed by user agents which
are compliant with the version of CSS Speech that supports
three-dimensional audio. In order to prepare for this possibility, the
values enabled by the current ‘<a href="#voice-balance"><code
class=property>voice-balance</code></a>’ property are designed to
remain compatible with "azimuth" angles. More precisely, the mapping
between the current left-right audio axis (lateral sound stage) and the
envisioned 360 degrees plane around the listener's position is defined as
follows:
<ul>
<li>The value ‘<code class=css>0</code>’ maps to zero degrees
(‘<code class=property>center</code>’). This is in "front" of
the listener, not from "behind".
<li>The value ‘<code class=css>-100</code>’ maps to -40
degrees (‘<code class=property>left</code>’). Negative angles
are in the counter-clockwise direction (the audio stage is seen from the
top).
<li>The value ‘<code class=css>100</code>’ maps to 40 degrees
(‘<code class=property>right</code>’). Positive angles are in
the clockwise direction (the audio stage is seen from the top).
<li>Intermediary values on the scale from ‘<code
class=css>-100</code>’ to ‘<code class=css>100</code>’
map to the angles between -40 and 40 degrees in a numerically
linearly-proportional manner. For example, ‘<code
class=css>-50</code>’ maps to -20 degrees.
</ul>
<p class=note> Note that sound systems may be configured by users in such a
way that it would interfere with the left-right audio distribution
specified by document authors. Typically, the various "surround&quo
7DF5
t; modes
available in modern sound systems (including systems based on basic stereo
speakers) tend to greatly alter the perceived spatial arrangement of audio
signals. The illusion of a three-dimensional sound stage is often achieved
using a combination of phase shifting, digital delay, volume control
(channel mixing), and other techniques. Some users may even configure
their system to "downgrade" any rendered sound to a single mono channel,
in which case the effect of the ‘<a href="#voice-balance"><code
class=property>voice-balance</code></a>’ property would obviously
not be perceivable at all. The rendering fidelity of authored content is
therefore dependent on such user customizations, and the ‘<a
href="#voice-balance"><code class=property>voice-balance</code></a>’
property merely specifies the desired end-result.
<p class=note> Note that many speech synthesizers only generate mono sound,
and therefore do not intrinsically support the ‘<a
href="#voice-balance"><code class=property>voice-balance</code></a>’
property. The sound distribution along the left-right axis consequently
occurs at post-synthesis stage (when the speech-enabled user agent mixes
the various audio sources authored within the document)
<h2 id=speaking-props><span class=secno>8. </span>Speaking properties</h2>
<h3 id=speaking-props-speak><span class=secno>8.1. </span>The ‘<a
href="#speak"><code class=property>speak</code></a>’ property</h3>
<table class=propdef summary="name: syntax">
<tbody>
<tr>
<td>Name:
<td> <dfn id=speak>speak</dfn>
<tr>
<td> <em>Value:</em>
<td>auto | none | normal
<tr>
<td> <em>Initial:</em>
<td>auto
<tr>
<td> <em>Applies to:</em>
<td>all elements
<tr>
<td> <em>Inherited:</em>
<td>yes
<tr>
<td> <em>Percentages:</em>
<td>N/A
<tr>
<td> <em>Media:</em>
<td>speech
<tr>
<td> <em>Computed value:</em>
<td>specified value
</table>
<p>The ‘<a href="#speak"><code class=property>speak</code></a>’
property determines whether or not to render text aurally.
<p class=note> Note that the functionality provided by this property has no
match in the SSML markup language <a href="#SSML"
rel=biblioentry>[SSML]<!--{{!SSML}}--></a>.
<dl>
<dt> <strong>auto</strong>
<dd>
<p>Resolves to a computed value of ‘<code
class=property>none</code>’ when <a
href="#display-def">‘<code
class=property>display</code>’</a> is ‘<code
class=property>none</code>’, otherwise resolves to a computed
value of ‘<code class=property>auto</code>’ which yields a
used value of ‘<code class=property>normal</code>’.</p>
<p class=note> Note that the ‘<code
class=property>none</code>’ value of the <a
href="#display-def">‘<code
class=property>display</code>’</a> property cannot be overridden
by descendants of the selected element, but the ‘<code
class=property>auto</code>’ value of ‘<a href="#speak"><code
class=property>speak</code></a>’ can however be overridden using
either of ‘<code class=property>none</code>’ or ‘<code
class=property>normal</code>’.</p>
<dt> <strong>none</strong>
<dd>
<p> This value causes an element (including pauses, cues, rests and
actual content) to not be rendered (i.e., the element has no effect in
the aural dimension).</p>
<p class=note> Note that any of the descendants of the affected element
are allowed to override this value, so descendants can actually take
part in the aural rendering despite using ‘<code
class=property>none</code>’ at this level. However, the pauses,
cues, and rests of the ancestor element remain "deactivated" in the
aural dimension, and therefore do not contribute to the <a
href="#collapsed-pauses">collapsing of pauses</a> or additive behavior
of adjoining rests.</p>
<dt> <strong>normal</strong>
<dd>
<p> The element is rendered aurally (regardless of its <a
href="#display-def">‘<code
class=property>display</code>’</a> value and the <a
href="#display-def">‘<code
class=property>display</code>’</a> and ‘<a
href="#speak"><code class=property>speak</code></a>’ values of its
ancestors).</p>
<p class=note> Note that using this value can result in the element being
rendered in the aural dimension even though it would not be rendered on
the visual canvas.</p>
</dl>
<h3 id=speaking-props-speak-as><span class=secno>8.2. </span>The ‘<a