Why do I get a crackle sometimes when playing back audio?

Issue Summary

A developer reported an issue with TTS (Text-to-Speech) audio crackling when played back through Twilio, but not locally. The TTS audio, after being generated, needed to be encoded in base64 before being sent via Twilio.

Hypothesis and Solution

It was hypothesized that the issue might be related to the = padding in base64 encoding, which is used to make the encoded string's length a multiple of four. This padding could become audible as a crackle when played back on Twilio.

The solution was to trim the = padding from the base64-encoded string before sending it through Twilio. After implementing this change, the crackle at the end of the audio playback was resolved.

Conclusion

Removing the base64 padding (=) from the encoded TTS audio before sending it to Twilio resolved the playback issue, eliminating the inconsistency and improving the audio quality.