Document:

<PAGE>

                                                                Exhibit 10.4

                          FIRST SUPPLEMENTAL INDENTURE

                         dated as of September 28, 2005

                                      among

                      CHARTER COMMUNICATIONS HOLDINGS, LLC,

               CHARTER COMMUNICATIONS HOLDINGS CAPITAL CORPORATION

                                       and

                            BNY MIDWEST TRUST COMPANY

                                   as Trustee

                          -----------------------------

                      9.92% Senior Discount Notes due 2011

<PAGE>

      THIS FIRST FIRST SUPPLEMENTAL INDENTURE (this "First Supplemental
Indenture"), entered into as of September 28, 2005, among Charter Communications
Holdings, LLC, a Delaware limited liability company (the "Company"), and Charter
Communications Holdings Capital Corporation, a company incorporated under the
laws of Delaware (collectively with the Company, the "Issuers"), and BNY Midwest
Trust Company (as successor to Harris Trust and Savings Bank), as trustee (the
"Trustee").

                                    RECITALS

      WHEREAS, the Issuers, Marcus Cable Holdings, LLC (which has subsequently
merged into the Company) and the Trustee entered into the Indenture, dated as of
March 17, 1999 (the "Indenture"; capitalized terms used herein without being
defined herein have the meanings given to them in the Indenture), relating to
the Company's 9.92% Senior Discount Notes due 2011 (the "Notes");

      WHEREAS, the Issuers desire to conform clause (1) of the definition of
"Permitted Investments" in the Indenture with the definitions contained in the
indentures of the Company's subsidiaries; and

      WHEREAS, in accordance with Section 9.02 of the Indenture, the Company has
obtained written consent to the proposed amendment from the Holders of a
majority in principal amount of the Notes then outstanding.

                                    AGREEMENT

      NOW, THEREFORE, in consideration of the premises and mutual covenants
herein contained and intending to be legally bound, the parties to this First
Supplemental Indenture hereby agree as follows:

      Section 1. Clause (1) of the definition of "Permitted Investments" in the
Indenture is hereby amended to read as follows:

            "(1) any Investment by the Company in a Restricted Subsidiary
            thereof, or any Investment by a Restricted Subsidiary of the Company
            in the Company or in another Restricted Subsidiary of the Company;".

      Section 2. This First Supplemental Indenture shall be governed by and
construed in accordance with the internal laws of the State of New York without
giving effect to the applicable principles of conflicts of laws to the extent
that the application of the laws of another jurisdiction would be required
thereby.

      Section 3. This First Supplemental Indenture may be signed in various
counterparts which together will constitute one and the same instrument. Each
signed copy shall be an original, but all of them together represent the same
agreement.

      Section 4. This First Supplemental Indenture is an amendment supplemental
to the Indenture, and the Indenture and this First Supplemental Indenture will
henceforth be read together.

<PAGE>

      Section 5. Except as expressly amended hereby, each provision of the
Indenture shall remain in full force and effect and, as amended hereby, the
Indenture is in all respects agreed to, ratified, and confirmed by each of the
Issuers and the Trustee.

      Section 6. The recitals contained herein shall be taken as the statements
of the Issuers, and the Trustee assumes no responsibility for their correctness.
The Trustee makes no representations as to the validity or sufficiency of this
First Supplemental Indenture.

                                       3

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

                                    Charter Communications Holdings, LLC, as
                                    Issuer

                                    By:  /s/ Thomas J. Hearity
                                         ----------------------------------
                                         Name: Thomas J. Hearity
                                         Title: SVP and Acting General Counsel

                                    Charter Communications Holdings Capital
                                    Corporation, as Issuer

                                    By:  /s/ Thomas J. Hearity
                                         ----------------------------------
                                         Name: Thomas J. Hearity
                                         Title: SVP and Acting General Counsel

                                    BNY Midwest Trust Company, as Trustee

                                    By:  /s/ Daniel G. Dwyer
                                         ----------------------------------
                                         Name: Daniel G. Dwyer
                                         Title: Vice President

                                       4<PAGE>

                                                                Exhibit 10.5

                          FIRST SUPPLEMENTAL INDENTURE

                         dated as of September 28, 2005

                                      among

                      CHARTER COMMUNICATIONS HOLDINGS, LLC,

               CHARTER COMMUNICATIONS HOLDINGS CAPITAL CORPORATION

                                       and

                            BNY MIDWEST TRUST COMPANY

                                   as Trustee

                          -----------------------------

                          10.00% Senior Notes due 2009

<PAGE>

      THIS FIRST FIRST SUPPLEMENTAL INDENTURE (this "First Supplemental
Indenture"), entered into as of September 28, 2005, among Charter Communications
Holdings, LLC, a Delaware limited liability company (the "Company"), and Charter
Communications Holdings Capital Corporation, a company incorporated under the
laws of Delaware (collectively with the Company, the "Issuers"), and BNY Midwest
Trust Company (as successor to Harris Trust and Savings Bank), as trustee (the
"Trustee").

                                    RECITALS

      WHEREAS, the Issuers and the Trustee entered into the Indenture, dated as
of January 12, 2000 (the "Indenture"; capitalized terms used herein without
being defined herein have the meanings given to them in the Indenture), relating
to the Company's 10.00% Senior Notes due 2009 (the "Notes");

      WHEREAS, the Issuers desire to conform clause (1) of the definition of
"Permitted Investments" in the Indenture with the definitions contained in the
indentures of the Company's subsidiaries; and

      WHEREAS, in accordance with Section 9.02 of the Indenture, the Company has
obtained written consent to the proposed amendment from the Holders of a
majority in principal amount of the Notes then outstanding.

                                    AGREEMENT

      NOW, THEREFORE, in consideration of the premises and mutual covenants
herein contained and intending to be legally bound, the parties to this First
Supplemental Indenture hereby agree as follows:

      Section 1. Clause (1) of the definition of "Permitted Investments" in the
Indenture is hereby amended to read as follows:

            "(1) any Investment by the Company in a Restricted Subsidiary
            thereof, or any Investment by a Restricted Subsidiary of the Company
            in the Company or in another Restricted Subsidiary of the Company;".

      Section 2. This First Supplemental Indenture shall be governed by and
construed in accordance with the internal laws of the State of New York without
giving effect to the applicable principles of conflicts of laws to the extent
that the application of the laws of another jurisdiction would be required
thereby.

      Section 3. This First Supplemental Indenture may be signed in various
counterparts which together will constitute one and the same instrument. Each
signed copy shall be an original, but all of them together represent the same
agreement.

      Section 4. This First Supplemental Indenture is an amendment supplemental
to the Indenture, and the Indenture and this First Supplemental Indenture will
henceforth be read together.

<PAGE>

      Section 5. Except as expressly amended hereby, each provision of the
Indenture shall remain in full force and effect and, as amended hereby, the
Indenture is in all respects agreed to, ratified, and confirmed by each of the
Issuers and the Trustee.

      Section 6. The recitals contained herein shall be taken as the statements
of the Issuers, and the Trustee assumes no responsibility for their correctness.
The Trustee makes no representations as to the validity or sufficiency of this
First Supplemental Indenture.

                                       3

<PAGE>

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

                                    Charter Communications Holdings, LLC, as
                                    Issuer

                                    By:  /s/ Eloise Schmitz
                                         ----------------------------------
                                         Name:  Eloise Schmitz
                                         Title: SVP Treasury and Finance

                                    Charter Communications Holdings Capital
                                    Corporation, as Issuer

                                    By:  /s/ Eloise Schmitz
                                         ----------------------------------
                                         Name: Eloise Schmitz
                                         Title:  SVP Treasury and Finance

                                    BNY Midwest Trust Company, as Trustee

                                    By:  /s/ Daniel G. Dwyer
                                         ----------------------------------
                                         Name: Daniel G. Dwyer
                                         Title: Vice President

                                       4

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