Workaround to enable the default volume to be adjusted.
Modifying the SSML volume definitions to match the default
volume.
diff --git a/pico/tts/svox_ssml_parser.cpp b/pico/tts/svox_ssml_parser.cpp
index 38d2f80..cc64d51 100755
--- a/pico/tts/svox_ssml_parser.cpp
+++ b/pico/tts/svox_ssml_parser.cpp
@@ -32,11 +32,11 @@
#define SSML_RATE_FAST "250"
#define SSML_RATE_XFAST "500"
#define SSML_VOLUME_SILENT "0"
-#define SSML_VOLUME_XLOW "20"
-#define SSML_VOLUME_LOW "60"
-#define SSML_VOLUME_MEDIUM "100"
-#define SSML_VOLUME_LOUD "300"
-#define SSML_VOLUME_XLOUD "450"
+#define SSML_VOLUME_XLOW "25"
+#define SSML_VOLUME_LOW "70"
+#define SSML_VOLUME_MEDIUM "250"
+#define SSML_VOLUME_LOUD "350"
+#define SSML_VOLUME_XLOUD "500"
#define SSML_BREAK_NONE "0ms"
#define SSML_BREAK_XWEAK "100ms"
#define SSML_BREAK_WEAK "300ms"