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Hydrogen-related infrared absorption bands in natural diamonds have been extensively investigated and widely used to identify natural, treated, and synthetic diamonds grown by high pressure and high temperature (HPHT) and chemical vapor deposition (CVD) techniques. However, the evolutional behavior of the hydrogen-related defects and the relationship between the hydrogen-related and nitrogen-related defects in natural and HPHT-treated Ib diamonds are unclear. In this article, the hydrogen-related defects, particularly the infrared absorption bands of 3107 cm⁻¹ and 3143 cm⁻¹ in natural type Ib diamonds and HPHT-treated natural diamonds, were systematically investigated using spectroscopic techniques. It was found that the 1405 cm⁻¹ absorption intensity was directly proportional to the 3107 cm⁻¹ absorption intensity; the 3143 cm⁻¹ absorption intensity increased with the increase in the 3107 cm⁻¹ absorption intensity, but there was no strict linear relationship between them. The 3143 cm⁻¹ band was not only related to the intensity of the 3107 cm⁻¹ but also related to the value of N_C/N_A in natural diamonds. When the value of N_C/N_A was less than one, the 3143 cm⁻¹ band was more pronounced. After high-temperature annealing, the absorption intensities of the 3107 cm⁻¹ and 3143 cm⁻¹ in natural type Ib diamonds became stronger. However, in HPHT synthetic diamonds, only a 3107 cm⁻¹ defect was introduced with the increase in the A centers in the diamonds. The difference and the detectability of the 3143 cm⁻¹ and 3107 cm⁻¹ bands investigated could be efficiently used to identify natural type Ib diamonds from their counterparts, including the synthetic diamonds and the HPHT-treated diamonds. Full article