Final answer:
The tag [inaudible] is used to denote speech that cannot be heard in a transcription due to noise or poor recording, which is impacted by the frequency and amplitude of the background noise.
Step-by-step explanation:
When speech cannot be heard due to poor recording or excessive noise, filmmakers and transcriptionists use the tag [inaudible] to indicate that the audio content could not be understood. This is especially common in environments with high noise levels, such as crowded roadways or areas with loud background noise, making it difficult to discern speech. The understanding of speech and its clarity is dependent on the frequency and amplitude of sound, with different challenges associated with hearing and recording in noisy environments.