THD is usually shown in negative dB. Most differential op amp datasheets only show distortion caused by the 2 nd harmonic (HD2) and 3 rd harmonic (HD3), as these are the main sources of distortion.

Harmonic distortion in amplifiers is usually caused by the amplifier needing more voltage than its power supply can provide. ... 1% THD is -40 dB below the original signal, ...

Audio Precision debuts APx555 with -120-dB THD+N typical. Sept. 9, 2014. Evaluation Engineering. September 9, 2014.

A critical measure for all audio components is distortion, typically specified as total harmonic distortion (THD) or total harmonic distortion + noise (THD+N). ... (typically >80 dB), ...

ESS Technology to Demonstrate SABRE9601, World’s Highest Performance SABRE Headphone Amplifier With 122dB DNR and -117dB THD at the Mobile World Congress 2014 Delivering Audiophile Quality Sound ...

ESS Technology Introduces the SABRE9602 at CES 2015: The World’s Highest Performance Headphone Amplifier with 122dB SNR, -123dB THD and Integrated Output Switch Audiophile High Quality Sound to ...