1
                                                                  EXHIBIT 10.4.4


                           FOURTH EXTENSION AGREEMENT

      Reference is made to that certain Credit Agreement by and between CRL
Systems, Inc. ("Borrower") and Harman Acquisition Corp. (f/k/a/ Orban, Inc.)
dated May 31, 2000 (the "Credit Agreement").

      1.    Lender shall extend the Tranche B Maturity Date to May 14, 2001.

      2.    Failure by Borrower or Circuit Research Labs, Inc. (the "Company")
            of any of its obligations under this Agreement shall be deemed an
            Event of Default under the Credit Agreement.

      3.    Borrower agrees that the Obligations are valid and enforceable
            obligations of Borrower and hereby confirms, acknowledges and
            ratifies the existence of the Obligations and Borrower's obligations
            to Lender with respect thereto as set forth in the Credit Agreement,
            and all other obligations of Borrower and the Company to Lender
            under the agreement among the parties hereto dated as of September
            29, 2000 (the "First Extension Agreement"), the agreement among the
            parties hereto dated as of November 28, 2000 (the "Second Extension
            Agreement"), the agreement among the parties dated as of February
            22, 2001 (the "Third Extension Agreement") and the Loan Documents.

      4.    THIS AGREEMENT, THE FIRST EXTENSION AGREEMENT, THE SECOND EXTENSION
            AGREEMENT, THE THIRD EXTENSION AGREEMENT AND THE OTHER LOAN
            DOCUMENTS REPRESENT THE FINAL AGREEMENT OF THE BORROWER AND THE
            LENDER WITH RESPECT TO THE SUBJECT MATTER HEREOF, AND THERE ARE NO
            PROMISES, UNDERTAKINGS, REPRESENTATIONS OR WARRANTIES BY THE LENDER
            RELATIVE TO THE SUBJECT MATTER HEREOF NOT EXPRESSLY SET FORTH OR
            REFERRED TO HEREIN OR IN THE OTHER LOAN DOCUMENTS.

      5.    Except as specifically set forth in this Agreement, the terms of the
            First Extension Agreement, the Second Extension Agreement, the Third
            Extension Agreement, the Loan Documents and the Warrant of the
            Company dated May 31, 2000 held by the Lender, will remain in full
            force and effect and are hereby ratified and confirmed.

      6.    This Agreement will be deemed to be a contract made under the Laws
            of the State of New York and for all purposes will be governed by
            and interpreted in accordance with the laws prevailing in the State
            of new York, without regard to principles of conflict of laws.

      7.    This Agreement may be executed in several counterparts each of which
            when so executed will be deemed to be an original and all of which
            will together constitute one and the same agreement.
   2
      8.    Capitalized terms used but not defined in this Agreement have the
            meanings ascribed to them in the Credit Agreement.

      IN WITNESS WHEREOF Borrower and Harman Acquisition Corp. executed this
Agreement as of February 22, 2001.

                                    CRL SYSTEMS, INC.


                                    By:  /s/ Charles Jayson Brentlinger
                                         ---------------------------------------
                                    Name: Charles Jayson Brentlinger
                                          --------------------------------------
                                    Title President, CEO, Chairman
                                          --------------------------------------

                                    HARMAN ACQUISITION CORP.


                                    By:  /s/ Frank Meredith
                                         ---------------------------------------
                                    Name:  Frank Meredith
                                           -------------------------------------
                                    Title:  CFO and Secretary
                                            ------------------------------------

Agreed to and accepted by

CIRCUIT RESEARCH LABS, INC.


By:  /s/ Charles Jayson Brentlinger
     --------------------------------------
Name: Charles Jayson Brentlinger
      -------------------------------------
Title:  President, CEO, Chairman
        -----------------------------------