Using custom audio files in custom Alexa skills adds a nice touch of originality and engagement. Developers with SSML know-how can easily personalize and brand their skill with custom audio MP3s. However, Amazon Alexa may often throw an error if you forget to convert your custom audio files to the specifications that are required.
The great people at Jovo (the company behind the Jovo Framework) have opened up a free service online for those of us who need to convert Alexa Skill audio files to the format Alexa expects. Not only do they convert the files to the appropriate format, they host it for you to download for 24 hours! You also can delete the file at any time that you choose.
NOTE: If you need to convert Alexa Skill audio files, it can be painful doing it yourself. If you need a simple buzzer or animal noise or another common sound, there are also built-in audio files published by Amazon that you can use. Check out this Alexa Skills Kit Sound Library reference for more files that can add some flair to your skill.