# Google Cloud Text-to-Speech API

#### Mark Edmondson

#### 2020-04-19

Google Cloud Text-to-Speech enables developers to synthesize natural-sounding speech with 30 voices, available in multiple languages and variants. It applies DeepMind’s groundbreaking research in WaveNet and Google’s powerful neural networks to deliver the highest fidelity possible. With this easy-to-use API, you can create lifelike interactions with your users, across many applications and devices.

Read more on the Google Cloud Text-to-Speech Website

The Cloud Text-to-Speech API turns text into sound files of the spoken words. Its accessible via the `gl_talk` function.

Arguments include:

- `input` - The text to turn into speech
- `output` Where to save the speech audio file
- `languageCode` The language of the voice as a `BCP-47` language tag
- `name` Name of the voice, see list via `gl_talk_languages()` or online for supported voices. If not set, then the service will choose a voice based on `languageCode` and `gender`.
- `gender` The gender of the voice, if available
- `audioEncoding` Format of the requested audio stream - can be a choice of `.wav`, `.mp3` or `.ogg`
- `speakingRate` Speaking rate/speed
- `pitch` Speaking pitch
- `volumeGainDb` Volumne gain in dB
- `sampleRateHertz` Sample rate for returned audio

## Returned structure

The API returns an audio file which is saved to the location specified in `output` - by default this is `output.wav` - if you don’t rename this file it will be overwritten by the next API call.

It is advised to set the appropriate file extension if you change the audio encoding (e.g. to one of `.wav`, `.mp3` or `.ogg`) so audio payers recognise the file format.

## Talk Languages

The API can talk several different languages, with more being added over time. You can get a current list via the function `gl_talk_languages()` or online

    gl_talk_languages()
    # A tibble: 32 x 4
       languageCodes name             ssmlGender naturalSampleRateHertz
       <chr>         <chr>            <chr>                       <int>
     1 es-ES         es-ES-Standard-A FEMALE                      24000
     2 ja-JP         ja-JP-Standard-A FEMALE                      22050
     3 pt-BR         pt-BR-Standard-A FEMALE                      24000
     4 tr-TR         tr-TR-Standard-A FEMALE                      22050
     5 sv-SE         sv-SE-Standard-A FEMALE                      22050
     6 nl-NL         nl-NL-Standard-A FEMALE                      24000
     7 en-US         en-US-Wavenet-A  MALE                        24000
     8 en-US         en-US-Wavenet-B  MALE                        24000
     9 en-US         en-US-Wavenet-C  FEMALE                      24000
    10 en-US         en-US-Wavenet-D  MALE                        24000

If you are looking a specific language, specify that in the function call e.g. to see only Spanish (`es`) voices issue:

    gl_talk_languages(languageCode = "es")
    # A tibble: 1 x 4
      languageCodes name             ssmlGender naturalSampleRateHertz
      <chr>         <chr>            <chr>                       <int>
    1 es-ES         es-ES-Standard-A FEMALE                      24000

You can then specify that voice when calling the API via the `name` argument, which overrides the `gender` and `languageCode` argument:

    gl_talk("Hasta la vista", name = "es-ES-Standard-A")

Otherwise, specify your own `gender` and `languageCode` and the voice will be picked for you:

    gl_talk("Would you like a cup of tea?", gender = "FEMALE", languageCode = "en-GB")

Some languages are not yet supported, such as Danish. The API will return an error in those cases.

## Support for SSML

Support is also included for Speech Synthesis Markup Language (SSML) - more details on using this to insert pauses, sounds and breaks in your audio can be found here: `https://cloud.google.com/text-to-speech/docs/ssml`

To use, send in your SSML markup around the text you want to talk and set `inputType= "ssml"`:

    # using SSML
    gl_talk('<speak>The <say-as interpret-as=\"characters\">SSML</say-as>
      standard <break time=\"1s\"/>is defined by the
      <sub alias=\"World Wide Web Consortium\">W3C</sub>.</speak>',
      inputType =  "ssml")

## Effect Profiles

You can output audio files that are optimised for playing on various devices.

To use audio profiles, supply a character vector of the available audio profiles listed here: `https://cloud.google.com/text-to-speech/docs/audio-profiles` - the audio profiles are applied in the order given.

For instance `effectsProfileIds="wearable-class-device"` will optimise output for smart watches, `effectsProfileIds=c("wearable-class-device","telephony-class-application")` will apply sound filters optimised for smart watches, then telephonic devices.

    # using effects profiles
    gl_talk("This sounds great on headphones",
            effectsProfileIds = "headphone-class-device")

## Browser Speech player

Creating and clicking on the audio file to play it can be a bit of a drag, so you also have a function that will play the audio file for you, launching via the browser. This can be piped via the tidyverse’s `%>%`

    library(magrittr)
    gl_talk("This is my audio player") %>% gl_talk_player()

    ## non-piped equivalent
    gl_talk_player(gl_talk("This is my audio player"))

The `gl_talk_player()` creates a HTML file called `player.html` in your working directory by default.

### Using with Shiny

You can do this in Shiny too, which is demonstrated in the example Shiny app included with the package.

Click the link for a video tutorial on how to integrate text-to-speech into a Shiny app - the demo uses text-to-speech to talk through a user’s Google Analytics statistics.

A shiny module has been created to help integrate text-to-speech into your Shiny apps, demo in the video above and below:

    library(shiny)
    library(googleLanguageR)  # assume auto auth setup

    ui <- fluidPage(
      gl_talk_shinyUI("talk")
    )

    server <- function(input, output, session){

         transcript <- reactive({
            paste("This is a demo talking Shiny app!")
         })

         callModule(gl_talk_shiny, "talk", transcript = transcript)
    }

    shinyApp(ui = ui, server = server)