Acquired identifiable intangible assets, and related accumulated amortization, as of March 31, 2021 and December 31, 2020 consist of:

	March 31, 2021
	Gross Carrying Value			Accumulated Amortization			Net Book Value
	(in thousands)
Customer relationships	$	8,355		$	5,760		$	2,595
Tradenames		3,066			500			2,566
Developed technology		1,884			238			1,646
Foreign currency		(804	)		(757	)		(47	)
Total Intangible Assets	$	12,501		$	5,741		$	6,760

	December 31, 2020
	Gross Carrying Value			Accumulated Amortization			Net Book Value
	(in thousands)
Customer relationships	$	7,915		$	5,584		$	2,331
Tradenames		2,686			425			2,261
Developed technology		784			177			607
Foreign currency		(845	)		(784	)		(61	)
Total Intangible Assets	$	10,540		$	5,402		$	5,138

In connection with the October 2012 acquisition of TB Europe, the acquired intangible assets related to customer relationships is being amortized over an estimated useful life of thirteen years with the amortization being included within sales and marketing expense.

In May 2019, the Company acquired the business and assets of ROCCAT. The acquired intangible assets of ROCCAT relating to developed technology, customer relationships and trade name are subject to amortization. In January 2021, the Company acquired the business and assets of Neat Microphones. The acquired intangible assets of Neat Microphones related to developed technology, customer relationships and trade name are subject to amortization. Refer to Note 3, “Acquisitions” for additional information related to Neat Microphone’s identifiable intangible assets.

Amortization expense related to definite lived intangible assets of $0.3 million was recognized for the three months ended March 31, 2021, and $0.2 million for the three months ended March 31, 2020.

As of March 31, 2021, estimated annual amortization expense related to definite lived intangible assets in future periods is as follows:

	(in thousands)
2021	$	988
2022		1,281
2023		1,041
2024		1,008
2025		889
Thereafter		1,600
Total	$	6,807

Changes in the carrying values of goodwill for the three months ended March 31, 2021 are as follows:

	(in thousands)
Balance as of January 1, 2021	$	8,178
Neat Microphones acquisition		2,508
Balance as of March 31, 2021	$	10,686