Sample Rate
The number of times per second an audio signal is measured during digital recording, with 44.1 kHz being the industry standard for audiobook production.
Sample rate is the number of discrete measurements (samples) taken of an analog audio signal per second during digital recording. A sample rate of 44,100 Hz (44.1 kHz) means the audio is measured 44,100 times every second. Higher sample rates capture more detail in the audio waveform, though the practical benefits diminish beyond the range of human hearing.
For audiobook production, 44.1 kHz is the industry standard. ACX, Audible, and the vast majority of audiobook distributors require it. This is the same sample rate used for CDs and provides frequency reproduction up to about 22 kHz, well above what humans can hear. It is the default you should use unless a publisher specifically tells you otherwise. The only common alternative is 48 kHz, which is the standard for video and broadcast work. Some publishers or studios may request 48 kHz for projects that will be synchronized with video content, but this is the exception rather than the rule.
It is important to record at the correct sample rate from the start. Converting between sample rates after recording (resampling) is detrimental to audio quality, and there is no benefit to recording at a higher rate and downsampling later for spoken-word content. If you are unsure which rate to use, choose 44.1 kHz. In Punch Track, the sample rate is set per project, ensuring every recording session for that book uses the correct rate from the first take.