Active voice liveness detection system

A computer-implemented method for detecting machine-based speech in calls, comprising:

• obtaining, by a computer, a verification prompt comprising challenge content for display at a user interface of a user device of a speaker;
• obtaining, by the computer, an input audio signal comprising a speech signal containing response content as an utterance of the speaker, wherein the response content in the speech signal purportedly matches to the challenge content of the verification prompt;
• extracting, by the computer, a text embedding using a first set of features extracted for the text of the challenge content of the verification prompt, and a spoken content embedding using a second set of features extracted using the speech signal of the input audio signal;
• and
• executing, by the computer, a content verification engine to generate a content verification score indicating a probability that the response content matches to the challenge content, the content verification engine having one or more layers of machine-learning architecture trained to determine a distance between the text embedding and a spoken content embedding and output the content verification score according to the distance.