chore: regens API reference docs (#889)

diff --git a/docs/dyn/texttospeech_v1beta1.text.html b/docs/dyn/texttospeech_v1beta1.text.html
index 05b90c0..2ce3423 100644
--- a/docs/dyn/texttospeech_v1beta1.text.html
+++ b/docs/dyn/texttospeech_v1beta1.text.html
@@ -75,16 +75,16 @@
 <h1><a href="texttospeech_v1beta1.html">Cloud Text-to-Speech API</a> . <a href="texttospeech_v1beta1.text.html">text</a></h1>
 <h2>Instance Methods</h2>
 <p class="toc_element">
-  <code><a href="#synthesize">synthesize(body, x__xgafv=None)</a></code></p>
+  <code><a href="#synthesize">synthesize(body=None, x__xgafv=None)</a></code></p>
 <p class="firstline">Synthesizes speech synchronously: receive results after all text input</p>
 <h3>Method Details</h3>
 <div class="method">
-    <code class="details" id="synthesize">synthesize(body, x__xgafv=None)</code>
+    <code class="details" id="synthesize">synthesize(body=None, x__xgafv=None)</code>
   <pre>Synthesizes speech synchronously: receive results after all text input
 has been processed.
 
 Args:
-  body: object, The request body. (required)
+  body: object, The request body.
     The object takes the form of:
 
 { # The top-level message sent by the client for the `SynthesizeSpeech` method.
@@ -99,14 +99,14 @@
       "text": "A String", # The raw text to be synthesized.
     },
     "voice": { # Description of which voice to use for a synthesis request. # Required. The desired voice of the synthesized audio.
-      "ssmlGender": "A String", # The preferred gender of the voice. Optional; if not set, the service will
+      "ssmlGender": "A String", # The preferred gender of the voice. If not set, the service will
           # choose a voice based on the other parameters such as language_code and
           # name. Note that this is only a preference, not requirement; if a
           # voice of the appropriate gender is not available, the synthesizer should
           # substitute a voice with a different gender rather than failing the request.
-      "languageCode": "A String", # The language (and optionally also the region) of the voice expressed as a
+      "languageCode": "A String", # Required. The language (and potentially also the region) of the voice expressed as a
           # [BCP-47](https://www.rfc-editor.org/rfc/bcp/bcp47.txt) language tag, e.g.
-          # "en-US". Required. This should not include a script tag (e.g. use
+          # "en-US". This should not include a script tag (e.g. use
           # "cmn-cn" rather than "cmn-Hant-cn"), because the script will be inferred
           # from the input provided in the SynthesisInput.  The TTS service
           # will use this parameter to help choose an appropriate voice.  Note that
@@ -115,42 +115,41 @@
           # (e.g. using en-US rather than en-CA if there isn't a Canadian voice
           # available), or even a different language, e.g. using "nb" (Norwegian
           # Bokmal) instead of "no" (Norwegian)".
-      "name": "A String", # The name of the voice. Optional; if not set, the service will choose a
+      "name": "A String", # The name of the voice. If not set, the service will choose a
           # voice based on the other parameters such as language_code and gender.
     },
     "audioConfig": { # Description of audio data to be synthesized. # Required. The configuration of the synthesized audio.
-      "audioEncoding": "A String", # Required. The format of the requested audio byte stream.
-      "effectsProfileId": [ # An identifier which selects 'audio effects' profiles that are applied on
-          # (post synthesized) text to speech.
-          # Effects are applied on top of each other in the order they are given.
-          # See
-          #
-          # [audio-profiles](https:
-          # //cloud.google.com/text-to-speech/docs/audio-profiles)
-          # for current supported profile ids.
+      "audioEncoding": "A String", # Required. The format of the audio byte stream.
+      "effectsProfileId": [ # Optional. Input only. An identifier which selects 'audio effects' profiles
+          # that are applied on (post synthesized) text to speech. Effects are applied
+          # on top of each other in the order they are given. See
+          # [audio
+          # profiles](https://cloud.google.com/text-to-speech/docs/audio-profiles) for
+          # current supported profile ids.
         "A String",
       ],
-      "sampleRateHertz": 42, # The synthesis sample rate (in hertz) for this audio. Optional.  If this is
-          # different from the voice's natural sample rate, then the synthesizer will
-          # honor this request by converting to the desired sample rate (which might
-          # result in worse audio quality), unless the specified sample rate is not
-          # supported for the encoding chosen, in which case it will fail the request
-          # and return google.rpc.Code.INVALID_ARGUMENT.
-      "pitch": 3.14, # Optional speaking pitch, in the range [-20.0, 20.0]. 20 means increase 20
-          # semitones from the original pitch. -20 means decrease 20 semitones from the
-          # original pitch.
-      "speakingRate": 3.14, # Optional speaking rate/speed, in the range [0.25, 4.0]. 1.0 is the normal
-          # native speed supported by the specific voice. 2.0 is twice as fast, and
-          # 0.5 is half as fast. If unset(0.0), defaults to the native 1.0 speed. Any
-          # other values < 0.25 or > 4.0 will return an error.
-      "volumeGainDb": 3.14, # Optional volume gain (in dB) of the normal native volume supported by the
-          # specific voice, in the range [-96.0, 16.0]. If unset, or set to a value of
-          # 0.0 (dB), will play at normal native signal amplitude. A value of -6.0 (dB)
-          # will play at approximately half the amplitude of the normal native signal
-          # amplitude. A value of +6.0 (dB) will play at approximately twice the
-          # amplitude of the normal native signal amplitude. Strongly recommend not to
-          # exceed +10 (dB) as there's usually no effective increase in loudness for
-          # any value greater than that.
+      "sampleRateHertz": 42, # Optional. The synthesis sample rate (in hertz) for this audio. When this is
+          # specified in SynthesizeSpeechRequest, if this is different from the voice's
+          # natural sample rate, then the synthesizer will honor this request by
+          # converting to the desired sample rate (which might result in worse audio
+          # quality), unless the specified sample rate is not supported for the
+          # encoding chosen, in which case it will fail the request and return
+          # google.rpc.Code.INVALID_ARGUMENT.
+      "pitch": 3.14, # Optional. Input only. Speaking pitch, in the range [-20.0, 20.0]. 20 means
+          # increase 20 semitones from the original pitch. -20 means decrease 20
+          # semitones from the original pitch.
+      "speakingRate": 3.14, # Optional. Input only. Speaking rate/speed, in the range [0.25, 4.0]. 1.0 is
+          # the normal native speed supported by the specific voice. 2.0 is twice as
+          # fast, and 0.5 is half as fast. If unset(0.0), defaults to the native 1.0
+          # speed. Any other values &lt; 0.25 or &gt; 4.0 will return an error.
+      "volumeGainDb": 3.14, # Optional. Input only. Volume gain (in dB) of the normal native volume
+          # supported by the specific voice, in the range [-96.0, 16.0]. If unset, or
+          # set to a value of 0.0 (dB), will play at normal native signal amplitude. A
+          # value of -6.0 (dB) will play at approximately half the amplitude of the
+          # normal native signal amplitude. A value of +6.0 (dB) will play at
+          # approximately twice the amplitude of the normal native signal amplitude.
+          # Strongly recommend not to exceed +10 (dB) as there's usually no effective
+          # increase in loudness for any value greater than that.
     },
   }
 
@@ -164,7 +163,8 @@
 
     { # The message returned to the client by the `SynthesizeSpeech` method.
     "audioContent": "A String", # The audio data bytes encoded as specified in the request, including the
-        # header (For LINEAR16 audio, we include the WAV header). Note: as
+        # header for encodings that are wrapped in containers (e.g. MP3, OGG_OPUS).
+        # For LINEAR16 audio, we include the WAV header. Note: as
         # with all bytes fields, protobuffers use a pure binary representation,
         # whereas JSON representations use base64.
   }</pre>