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# Audio Quality Guidelines

This appendix describes the audio properties required for accurate speech processing.

Several factors affect the recall rate (correct detection) of words or phrases:

- Signal bandwidth
- Background noise
- Speech clarity, which can be affected by factors such as whether a speaker is native
- Audio signal distortion, due to compression and storage
- Breadth of language context

For best speech processing results, ensure that your audio conforms to the following guidelines:

- The sampling frequency must be at least the sampling frequency required by the processing task. Audio files with sampling frequencies below this are upsampled, which causes severe quality issues. The minimum sampling frequencies are 8 kHz for telephony audio and 16 kHz for broadcast audio.
- The minimum SNR (signal-to-noise ratio) is 15 dB. An SNR of 25 dB or above produces the best results. This ratio is measured across the word or phrase being detected and not across the entire audio.
- Words or phrases must be articulated reasonably clearly, and largely conform to the language. Speech-to-text performance is known to be poorer for non-native speakers than for native speakers.
- Natural speech rates produce the best speech-to-text results. Speech that is faster or slower than this usually produces more errors.
- When word confidences are enabled, every recognized word is associated with an acoustic confidence value. Generally, false positives tend to have a lower acoustic confidence compared to true hits.
- Newer audio codecs offer less distortion for the same rate of compression.
- If the language context of the content is too broad, the effectiveness of the language model is reduced.

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