Some time back Google pushed out an update allowing you to switch between the female voice (Voice I) and the male voice (Voice II). Following these instructions in order to activate them:
You will be able to hear the female or male voice on all of your Assistant devices once you set the voice. In case you are not able to see the option at the moment make sure to update the Google and Home apps first. If that is not the problem you will have to wait for some time as the feature is likely to be available to all before Google’s Pixel 2 event.
In order to switch between female and male Google Assistant voices you need to launch the Home app and tap on the Menu icon. Under the Google Assistant subheading, you need to choose More settings and then below Account, tap on Preferences. The next thing to do is to choose Assistant voice. You will see a list of available voices here.
In order to preview each voice you can tap on the blue speaker icon. You can choose the voice name you want to set for all of your devices with Assistant built-in.