SUPPLEMENTAL INDENTURE
                            ----------------------


            SUPPLEMENTAL INDENTURE (this "Supplemental Indenture"), dated as of
March 24, 2000 among Vortex Sound Communications Company, Inc., a Delaware
corporation (the "New Guarantor"), a subsidiary of Muzak LLC (or its successor),
a Delaware limited liability company (the "Company"), Muzak Finance Corp., a
Delaware corporation ("Finance Corp.", and together with the Company, the
"Issuers"), the Guarantors (the "Existing Guarantors") under the Indenture
referred to below, and State Street Bank and Trust Company, as trustee under the
Indenture referred to below (the "Trustee").

                             W I T N E S S E T H :
                             -------------------

            WHEREAS the Issuers have heretofore executed and delivered to the
Trustee an Indenture (as such may be amended from time to time, the
"Indenture"), dated as of February 2, 2000, providing for the issuance of up to
an aggregate principal amount of $50,000,000 of Senior Subordinated Floating
Rate Notes due 2009 (the "Notes");

            WHEREAS Section 4.22 of the Indenture provides that under certain
circumstances the Issuers are required to cause the New Guarantor to execute and
deliver to the Trustee a supplemental indenture pursuant to which the New
Guarantor shall unconditionally guarantee all of the Issuers, obligations under
the Notes pursuant to a Guarantee on the terms and conditions set forth herein;
and

            WHEREAS pursuant to Section 8.01 of the Indenture, the Trustee, the
Issuers and Existing Guarantors are authorized to execute and deliver this
Supplemental Indenture;

            NOW THEREFORE, in consideration of the foregoing and for other good
and valuable consideration, the receipt of which is hereby acknowledged, the New
Guarantor, the Issuers, the Existing Guarantors and the Trustee mutually
covenant and agree for the equal and ratable benefit of the Noteholders as
follows:

            1. Definitions. (a) Capitalized terms used herein without definition
shall have the meanings assigned to them in the Indenture.

            (b) For all purposes of this Supplemental Indenture, except as
otherwise herein expressly provided or unless the context otherwise requires:
(i) the terms and expressions used herein shall have the same meanings as
corresponding terms and expressions used in the Indenture; and (ii) the words
"herein", "hereof" and "hereby" and other words of similar import used in this
Supplemental Indenture refer to this Supplemental Indenture as a whole and not
to any particular section hereof.
<PAGE>
            2. Agreement to Guarantee. The New Guarantor hereby agrees, jointly
and severally with all other Guarantors, to guarantee the Issuers' obligations
under the Indenture and the Notes on the terms and subject to the conditions set
forth in Article 10 of the Indenture, and to be bound by all of said Article 10,
as a "Guarantor" thereunder, and to be bound by all other applicable provisions
of the Indenture. From and after the date hereof, the New Guarantor shall be a
Guarantor for all purposes under the Indenture and the Notes.

            3. Ratification of Indenture; Supplemental Indentures; Part of
Indenture. Except as expressly amended hereby, the Indenture is in all respects
ratified and confirmed and all the terms, conditions and provisions thereof
shall remain in full force and effect. This Supplemental Indenture shall form a
part of the Indenture for all purposes, and every Noteholder heretofore or
hereafter authenticated and delivered shall be bound hereby.

            4. Governing Law. THIS SUPPLEMENTAL INDENTURE SHALL BE GOVERNED BY,
AND CONSTRUED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF NEW YORK BUT WITHOUT
GIVING EFFECT TO APPLICABLE PRINCIPLES OF CONFLICTS OF LAW.

            5. Trustee Makes No Representation. The Trustee makes no
representation as to the validity or sufficiency of this Supplemental Indenture.

            6. Counterparts. The parties may sign any number of copies of this
Supplemental Indenture. Each signed copy shall be an original, but all of them
together represent the same agreement.

            7. Effect of Headings. The Section headings herein are for
convenience only and shall not affect the construction thereof.

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<PAGE>
            IN WITNESS WHEREOF, the parties hereto have caused this Supplemental
Indenture to be duly executed as of the date first above written.


                                           VORTEX SOUND COMMUNICATIONS
                                           COMPANY, INC.


                                           By: /s/ Peni Garber
                                              _________________________
                                              Name:  Peni Garber
                                              Title: Vice President

                                           MUZAK LLC


                                           By: /s/ Peni Garber
                                              ______________________
                                              Name:  Peni Garber
                                              Title: Vice President

                                           MUZAK FINANCE CORP.


                                           By: /s/ Peni Garber
                                              ______________________
                                              Name:  Peni Garber
                                              Title: Vice President

                                           EXISTING GUARANTORS:

                                           MUZAK HOLDINGS LLC


                                           By: /s/ Peni Garber
                                              ______________________
                                              Name:  Peni Garber
                                              Title: Vice President

                                           MUZAK CAPITAL CORPORATION


                                           By: /s/ Peni Garber
                                              ______________________
                                              Name:  Peni Garber
                                              Title: Vice President


                                           MLP ENVIRONMENTAL MUSIC, LLC

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<PAGE>
                                           By: /s/ Peni Garber
                                              ______________________
                                              Name:  Peni Garber
                                              Title: Vice President

                                           BUSINESS SOUND INC.


                                           By: /s/ Peni Garber
                                              ______________________
                                              Name:  Peni Garber
                                              Title: Vice President

                                           BACKGROUND MUSIC
                                           BROADCASTERS, INC.


                                           By: /s/ Peni Garber
                                              ______________________
                                              Name:  Peni Garber
                                              Title: Vice President

                                           AUDIO ENVIRONMENTS, INC.


                                           By: /s/ Peni Garber
                                              ______________________
                                              Name:  Peni Garber
                                              Title: Vice President

                                           TELEPHONE AUDIO
                                           PRODUCTIONS, INC.


                                           By: /s/ Peni Garber
                                              ______________________
                                              Name:  Peni Garber
                                              Title: Vice President

                                           STATE STREET BANK AND TRUST
                                           COMPANY, as Trustee


                                           By: /s/ Jacqueline A. Bonhomme
                                              ____________________________
                                              Name: Jacqueline A. Bonhomme
                                              Title: Assistant Vice President


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