<PAGE>   1
                                                                   EXHIBIT 10.33

THE SECURITY EVIDENCED BY THIS NOTE AND THE SECURITIES ISSUABLE UPON CONVERSION
OF THIS NOTE HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS
AMENDED, AND MAY NOT BE SOLD, TRANSFERRED OR ASSIGNED UNLESS THERE IS AN
EFFECTIVE REGISTRATION STATEMENT UNDER SUCH ACT COVERING SUCH SECURITIES, THE
SALE, TRANSFER OR ASSIGNMENT IS MADE IN ACCORDANCE WITH RULE 144 UNDER THE ACT,
OR THE COMPANY RECEIVES AN OPINION OF COUNSEL FOR THE HOLDER OF THESE SECURITIES
REASONABLY SATISFACTORY TO THE COMPANY, STATING THAT SUCH SALE, TRANSFER OR
ASSIGNMENT IS EXEMPT FROM THE REGISTRATION AND PROSPECTUS DELIVERY REQUIREMENTS
OF SUCH ACT.


                             SECURED PROMISSORY NOTE

Four Hundred Thousand Dollars
($400,000.00)                                                  September 7, 2000



A.      Principal and Interest. For value received, the undersigned, Euphonix,
Inc., a California corporation ("Borrower"), hereby promises to pay to Walter
Bosch ("Lender"), or his registered assigns, the principal sum of Four Hundred
Thousand Dollars ($400,000). Interest shall accrue with respect to the
outstanding principal hereunder at the per annum rate of eight percent (8.00%),
net of any deductions or withholding taxes. Interest payable hereunder shall be
calculated on the basis of a three hundred sixty (360) day year for actual days
elapsed. Interest shall be due and payable (or converted as set forth in Section
B below) upon payment or conversion of the principal sum of this Note pursuant
to Section B below. Notwithstanding the foregoing to the contrary, during any
period for which an Event of Default shall have occurred and be continuing,
interest shall accrue with respect to the outstanding principal amount hereunder
at the per annum rate of fourteen percent (14.00%), net of any deductions or
withholding taxes.

B.      Payment or Conversion.

        1.      Scheduled Payment. Subject to other provisions of this Note, the
outstanding principal sum of this Note, together with the accrued interest
thereon, shall be due and payable on July 31, 2001.

        2.      No Prepayment. Borrower shall not have the right at any time to
time to prepay, in whole or in part, the outstanding principal sum of this Note
and/or any accrued interest thereon.

        3.      Form of Payment. Unless converted pursuant to the terms set
forth below, the outstanding principal sum and accrued interest thereon are to
be paid in lawful money of the United States of America in federal or other
immediately available funds.

        4.      Immediate Payment. Notwithstanding anything herein to the
contrary, in the event that all necessary shareholder, regulatory and other
approvals or consents for the convertibility of this Note as set forth below are
not obtained by July 31, 2001, the outstanding principal amount and

<PAGE>   2


accrued interest thereon, shall be repaid in full upon demand by the Lender;
provided, however, that the Lender must provide at least one (1) month prior
written notice to the Borrower prior to such demand. In addition, such demand
may not be made (x) if shareholder approval for the convertibility of this Note
is not obtained as a result of the Lender failing to vote or consent for such
convertibility, or (y) if shareholder approval for the convertibility of this
Note would not be required so long as the Borrower obtain shareholder approval
with respect to such other security issuances by the Borrower, but shareholder
approval with respect to such other issuances not be obtained as a result of the
investors failing to vote or consent with respect to such other issuances.

        5.     Conversion.

               (a) Subject to obtaining all necessary shareholders, regulatory
and other approvals or consents and further subject to Section B.5(c) hereof,
all or part of the principal sum of this Note, together with the accrued
interest thereon, shall be convertible at the option of the Lender into shares
of common stock of the Borrower (the "Common Stock"). The number of shares of
Common Stock to be issued upon such conversion(s) shall be equal to the quotient
obtained by dividing (i) such part (or all) of the principal sum of this Note
plus accrued interest thereon by (ii) the average closing bid price for the
Common Stock for the ten trading days immediately preceding the day of execution
of this Note, which is $2.3562 per share (the "Purchase Price").

               (b) No fractional share of Common Stock will be issued upon such
conversion(s) of this Note. In lieu of any fractional share to which the Lender
would otherwise be entitled, the Borrower will pay to the Lender in cash the
amount of the unconverted principal and interest balance of this Note that would
otherwise be converted into such fractional share. At its expense, the Borrower,
will as soon as practicable thereafter, issue and deliver to the Lender, at its
principal office, or other address notified by the Lender to the Borrower from
time to time, a certificate or certificates for the number of shares
(representing its pro rata portion) to which the Lender is entitled upon such
conversion(s). Upon such conversion(s) of this Note, the Borrower will be
forever released from all of its obligations and liabilities under this Note, to
the extent of the conversion. Such conversions may be exercised individually by
the Lender but notwithstanding anything herein to the contrary, each such
conversion must be for the full amount of the outstanding principal and accrued
interest thereon payable to the Lender exercising its rights under Section B.5
hereunder at the time of such exercise.

               (c) Notwithstanding anything herein to the contrary, Section
B.5(a) of this Note shall not apply and this Note shall not be convertible into
shares of Common Stock as contemplated herein (i) until such time as the
Borrower has obtained shareholder approval of the conversion feature of this
Note as and to the extent required by the rules of the National Association of
Securities Dealers; and (ii) upon the occurrence of the following: the
consummation of any transaction or series of transactions (collectively, the
"Transaction"), including without limitation, the sale, transfer or disposition
of all or substantially all of the Borrower's assets or the merger of the
Borrower with or into, or consolidation with, any other corporate entity,
whereby the holders of the Borrower's voting securities prior to the Transaction
do not hold more than 50% of the voting securities of the surviving entity
following the consummation of the Transaction. Notice of any such Transaction
shall be provided to the Lender fourteen (14) calendar days prior to the
consummation


                                      -2-
<PAGE>   3

of any such Transaction and, notwithstanding anything to the contrary contained
elsewhere in this Note, Lender may exercise his rights of conversion during such
14-day period.

C.      Security Interest.

        1.      Grant of Security Interest. Borrower grants to Lender a security
interest in the Collateral, as defined herein, to secure the payment of all of
the outstanding indebtedness hereunder (the "Secured Obligations") including,
without limitation, principal and accrued interest and any attorneys' fees to
which Lender is entitled under this Note.

        2.      Representations and Warranties Regarding Collateral. On the date
of this Note, Borrower does and shall represent and warrant to Lender, that as
of such date:

                (a) Borrower is the true and lawful owner of the Collateral,
having good and marketable title thereto, free and clear of any and all Liens
other than the Lien and security interest granted to Lender hereunder and
Permitted Liens.

                (b) The lien against the Collateral granted hereunder is and
shall be a first-priority lien against the collateral and each portion thereof,
subject to Permitted Liens.

                (c) Borrower shall not create or assume or permit to exist any
such Lien on or against any of the Collateral except as created or permitted by
this Note and Permitted Liens, and Borrower shall promptly notify Lender of any
such other Lien against the Collateral and shall defend the Collateral against,
and take all such action as may be reasonably necessary to remove or discharge,
any such Lien.

                (d) Borrower shall take all commercially reasonable actions
necessary to protect and preserve the Collateral which is used in its business
in good condition and repair, subject to ordinary wear and tear, and to preserve
its value and usefulness.

                (e) No part of the Intellectual Property Collateral has been
judged invalid or unenforceable, in whole or in part.

                (f) No claim has been made that any part of the Intellectual
Property Collateral violates the rights of any third party.

                (g) The Collateral consists of all assets which are required for
the conduct and operation of the business of Borrower as of the date of this
Note.

                (h) The Intellectual Property Collateral includes all of the
technology, know-how and proprietary information which are required for the
conduct and operation of the business of borrower as of the date of this Note.

        3.      General Representations and Warranties. On the date of this
Note, Borrower does and shall represent and warrant to Lender, that as of such
date:

                                      -3-
<PAGE>   4


                (a) ORGANIZATION AND QUALIFICATION. Borrower is a corporation
duly organized, validly existing and in good standing under the laws of the
State of California. Borrower has the requisite corporate power and authority to
own, operate or lease its properties and to carry on its business as it is now
being conducted and is duly qualified or licensed to do business, and is in good
standing, in each jurisdiction in which the nature of its business or the
properties owned, operated or leased by it makes such qualification, licensing
or good standing necessary, except where the failure to have such power or
authority, or the failure to be so qualified, licensed or good standing
necessary, except where the failure to have such power or authority, or the
failure to be so qualified, licensed or in good standing, would not have a
Material Adverse Effect.

                The term "Material Adverse Effect," as used in this Note, means
any change in or effect (or any development that is reasonably likely to result
in any change or effect) on the business, business prospects, properties,
assets, operations, financial condition or results of operations of Borrower
that is materially adverse to Borrower taken as a whole.

                (b) AUTHORITY RELATIVE TO THIS NOTE. This Note has been duly and
validly authorized, executed and delivered by Borrower and constitutes a valid
and binding obligation of Borrower enforceable against Borrower in accordance
with its terms, except that such enforceability (i) may be limited by
bankruptcy, insolvency, moratorium or other similar laws affecting or relating
to the enforcement of creditors' rights generally and (ii) is subject to general
principles of equity.

                (c) NO CONFLICT; REQUIRED FILINGS AND CONSENTS. Except for the
approval of Shareholders contemplated under Section B, none of the execution and
delivery of this Note by Borrower, the consummation by Borrower of the
transactions contemplated hereby or compliance by Borrower with any of the
provisions hereof will (i) conflict with or violate the certificate of
incorporation or by-laws of Borrower, (ii) conflict with or violate any material
statute, ordinance, rule, regulation, order, judgment or decree applicable to
Borrower, or by which Borrower or its properties or assets may be bound, or
(iii) result in a violation or breach of or constitute a default (or an event
which with notice or lapse of time or both would become a default) under, or
give to others any rights of termination, amendment, acceleration or
cancellation of, or result in any loss of any material benefit, or the creation
of any lien on any of the property or assets of Borrower pursuant to any
material agreement, a copy of which would be required to be filed as an exhibit
to the Company's Form 10-K or Form 10-Q filed with the Securities and Exchange
Commission (the "Commission") pursuant to the Securities Exchange Act of 1934,
as amended (the "Exchange Act").

                (d) CONSENTS. None of the execution and delivery of this Note by
Borrower, the consummation by Borrower of the transactions contemplated hereby
or compliance by Borrower with any of the provisions hereof will require any
consent, waiver, approval, authorization or permit of, or registration or filing
with or notification to (any of the foregoing being a "Consent"), any government
or subdivision thereof, or any administrative, governmental or regulatory
authority, agency, commission, tribunal or body, domestic, foreign or
supranational (a "Governmental Entity"), except for Consents the failure of
which to obtain or make would not have a Material Adverse Effect or adversely
affect the ability of Borrower to consummate the transactions contemplated
hereby; provided, that the convertibility feature of this Note as set forth in
Section B, which requires shareholder approval pursuant to the Nasdaq Stock
Market's shareholder approval provisions, is obtained.

                                      -4-
<PAGE>   5

                (e) MATERIAL ADVERSE CHANGE. Since the date of the latest
financial statements filed by Borrower with the Commission prior to the date of
this Note, there has not been any event, occurrence or development that has
resulted or, to the Company's knowledge, is reasonably likely to result in a
Material Adverse Effect.

        4.      Perfection of Security Interest. Borrower agrees to take all
actions required or requested by Lender and reasonably necessary to perfect, to
continue the perfection of, and to otherwise give notice of, the Lien granted
hereunder, including, but not limited to, execution and filing of financing
statements and the filing of notices of security interests with the United
States Patent and Trademark Office.

D.      Events of Default.

        1.      Definition of Event of Default. The occurrence of any one or
more of the following events shall constitute an "Event of Default" hereunder:

                (a) Borrower's failure to perform, keep or observe any
obligation under this Note or any of the covenants contained in this Note which
failure is not cured within 30 days from the notice of the occurrence thereof
delivered by Lender to Borrower.

                (b) The lapse of 60 days following the institution of
proceedings against Borrower, or Borrower's filing of a petition or answer or
consent seeking reorganization or release, under the federal Bankruptcy Code, or
any other applicable federal or state law relating to creditor rights and
remedies, or Borrower's consent to the filing of any such petition or the
appointment of a receiver, liquidator, assignee, trustee or other similar
official of Borrower or of any substantial part of its property, or Borrower's
making of an assignment for the benefit of creditors, or the taking of corporate
action in furtherance of such action.

                (c) Any representation or warranty of the Borrower made in this
Note proves untrue in any material respect as of the date of the issuance or
making thereof.

        2.      Rights and Remedies on Event of Default.

                (a) During the continuance of an Event of Default, Lender shall
have the right, itself or through any of its agents, with notice to Borrower (as
provided below), as to any or all of the Collateral, by any available judicial
procedure, or without judicial process (provided, however, that it is in
compliance with the UCC), declare all obligations evidenced by this Note
immediately due and payable, cease advancing money or extending credit to or for
the benefit of Borrower under this Note, and to exercise any and all rights
afforded to a secured party under the UCC or other applicable law. Without
limiting the generality of the foregoing, Lender shall have the right to sell or
otherwise dispose of all or any part of the Collateral, either at public or
private sale, in lots or in bulk, for cash or for credit, with or without
warranties or representations, and upon such terms and conditions, all as
Lender, in its reasonable discretion, may deem advisable, and it shall have the
right to purchase at any such sale. Borrower agrees that a notice sent at least
fifteen (15) days before the time of any intended public sale or of the time
after which any private sale or other disposition of the Collateral is to be
made shall be reasonable notice of such sale or other disposition. The proceeds
of


                                      -5-
<PAGE>   6

any such sale, or other Collateral disposition shall be applied, first to the
expenses of retaking, holding, storing, processing and preparing for sale,
selling, and the like, and to Lender's reasonable attorneys' fees and legal
expenses, and then to the Secured Obligations and to the payment of any other
amounts required by applicable law, after which Lender shall account to Borrower
for any surplus proceeds. If, upon the sale or other disposition of the
Collateral, the proceeds thereof are insufficient to pay all amounts to which
Lender is legally entitled, Borrower shall be liable for the deficiency,
together with interest thereon, and the reasonable fees of any attorneys Lender
employs to collect such deficiency; provided, however that the foregoing shall
not be deemed to require Lender to resort to or initiate proceedings against the
Collateral prior to the collection of any such deficiency or other amount
directly from Borrower.

                (b) Borrower appoints Lender, and any officer, employee or agent
of Lender, with full power of substitution, as Borrower's true and lawful
attorney-in-fact, effective as of the date hereof, with power, in its own name
or in the name of Borrower, during the continuance of an Event of Default, to
endorse any notes, checks, drafts, money orders, or other instruments of payment
in respect of the Collateral that may come into Lender's possession, to sign and
endorse any drafts against debtors, assignments, verifications and notices in
connection with accounts, and other documents relating to Collateral; to pay or
discharge taxes or Liens at any time levied or placed on or threatened against
the Collateral; to demand, collect, issue receipt for, compromise, settle and
sue for monies due in respect of the Collateral; to notify persons and entities
obligated with respect to the Collateral to make payments directly to Lender;
and, generally, to do, at Lender's option and at Borrower's expense, at any
time, or from time to time, all acts and things which Lender deems necessary to
protect, preserve and realize upon the Collateral and Lender's security interest
therein to effect the intent of this Note, all as fully and effectually as
Borrower might or could do; and Borrower hereby ratifies all that said attorney
shall lawfully do or cause to be done by virtue hereof. This power of attorney
shall be irrevocable as long as any of the Secured Obligations are outstanding.

                (c) All of Lender's rights and remedies with respect to the
Collateral, whether established hereby or by any other agreements, instruments
or documents or by law shall be cumulative and may be exercised singly or
concurrently.

                (d) Upon the occurrence of an Event of Default, the Lender may
bring suit against Borrower to collect amounts due the Lender under this Note.

E.      Restrictions on Transfer and Compliance with Securities Act.

        1.      Certificates. Certificates representing any of the shares of
Common Stock acquired pursuant to the provisions of this Note shall have
endorsed thereon the following legends, as appropriate.

                (a) Such shares of Common Stock will not be registered under the
Securities Act of 1933, as amended (the "Securities Act"), nor qualified (if
necessary) under applicable state securities laws and consequently will have the
following legend:

                                      -6-
<PAGE>   7

        "THE SECURITIES EVIDENCED BY THIS CERTIFICATE HAVE NOT BEEN REGISTERED
        UNDER THE SECURITIES ACT OF 1933, AS AMENDED, AND MAY NOT BE SOLD,
        TRANSFERRED, ASSIGNED OR HYPOTHECATED UNLESS THERE IS AN EFFECTIVE
        REGISTRATION STATEMENT UNDER SUCH ACT COVERING SUCH SECURITIES, THE SALE
        IS MADE IN ACCORDANCE WITH RULE 144 UNDER THE ACT, OR THE COMPANY
        RECEIVES AN OPINION OF COUNSEL FOR THE HOLDER OF THESE SECURITIES
        REASONABLY SATISFACTORY TO THE COMPANY, STATING THAT SUCH SALE,
        TRANSFER, ASSIGNMENT OR HYPOTHECATION IS EXEMPT FROM THE REGISTRATION
        AND PROSPECTUS DELIVERY REQUIREMENTS OF SUCH ACT."

                (b) Any legend required to be placed thereon by any applicable
state securities laws.

        2.      The Lender, by acceptance hereof, agrees that this Note and the
shares of Common Stock to be issued upon conversion pursuant to the terms hereof
are being acquired solely for its own account and not as a nominee for any other
party and not with a view toward the resale or distribution thereof and that it
will not offer, sell or otherwise dispose of this Note or any shares of Common
Stock to be issued upon conversion pursuant to the terms hereof except under
circumstances which will not result in a violation of the Securities Act or of
applicable state securities laws.

        3.      The Lender, by acceptance hereof, represents that the Lender is
(i) an accredited investor within the meaning of Rule 501 under the Securities
Act and has such knowledge and experience in financial and business matters that
it is capable of evaluating the merits and risks of the purchase of the Note;
(ii) aware of the Company's business affairs and financial condition; and (iii)
aware that the Note has not been registered under the Securities Act of 1933, as
amended, in reliance upon a specific exemption therefrom.

        4.      Subject to the preceding, this Note may be transferred only upon
surrender of the original Note for registration of transfer, duly endorsed, or
accompanied by a duly executed written instrument of transfer in form
satisfactory to Borrower. Thereupon, a new Note for like principal amount and
interest will be issued to, and registered in the name of, the transferee.
Interest and principal are payable only to the registered holder of the Note.

F.      Covenants.

        1.      Registration Rights. Upon receipt of the necessary approvals for
the convertibility feature of this Note set forth in Section B.5 above, the
Borrower hereby covenants to enter into a registration rights agreement with the
Lender to provide for the registration of the shares of Common Stock into which
the Note is then convertible, in the form set forth on Exhibit B hereto.

        2.      Warrants. In the event the Lender shall elect to convert all or
a portion of its Pro Rata Share of this Note into Common Stock in accordance
with Section C.5 above, the Borrower shall

                                      -7-
<PAGE>   8

issue to the Lender warrants to purchase shares of common stock, in the form set
forth on Exhibit C hereto.

G.      Other Provisions.

        1.      Definitions. As used herein, the following terms shall have the
following meanings:

                "Collateral" means the property described on Exhibit A attached
hereto.

                "Copyrights" means any and all copyright rights, copyright
applications, copyright registrations and like protections in each work or
authorship and derivative work thereof, whether published or unpublished and
whether or not the same also constitutes a trade secret, now or hereafter
existing, created, acquired or held.

                "Intellectual Property Collateral" means:

                (a) Copyrights, Trademarks and Patents;

                (b) Any and all trade secrets, and any and all intellectual
property rights in computer software and computer software products now or
hereafter existing, created, acquired or held;

                (c) Any and all design rights which may be available to Borrower
now or hereafter existing, created, acquired or held;

                (d) Any and all claims for damages by way of past, present and
future infringement of any of the rights included above, with the right, but not
the obligation, to sue for and collect such damages for said use or infringement
of the intellectual property rights identified above;

                (e) All licenses or other rights to use any of the Copyrights,
Patents or Trademarks, and all license fees and royalties arising from such use
to the extent permitted by such license or rights;

                (f) All amendments, renewals and extensions of any of the
Copyrights, Trademarks or Patents; and

                (g) All proceeds and products of the foregoing, including
without limitation all payments under insurance or any indemnity or warranty
payable in respect of any of the foregoing.

                "Lien" means any lien (statutory or other), mortgage, pledge,
hypothecation, assignment, deposit arrangement, security interest, charge, claim
or other encumbrance of any kind (including any conditional sale or other title
retention agreement, any lease in the nature thereof, and any agreement to give
any security interest) and any agreement to give or refrain from giving a lien,
mortgage, pledge, hypothecation, assignment, deposit arrangement, security
interest, charge, claim or other encumbrance of any kind.

                                      -8-
<PAGE>   9

                "Patents" means all patents, patent applications and like
protections including without limitation improvements, divisions, continuations,
renewals, reissues, extensions and continuations in part of the same.

                "Permitted Liens" means: (i) Liens imposed by law, such as
carriers', warehousemen's, materialmen's and mechanics' liens, or Liens arising
out of judgments or awards against Borrower with respect to which Borrower at
the time shall currently be prosecuting an appeal or proceedings for review;
(ii) Liens for taxes not yet subject to penalties for nonpayment and Liens for
taxes the payment of which is being contested in good faith and by appropriate
proceedings and for which, to the extent required by generally accepted
accounting principles then in effect, proper and adequate book reserves relating
thereto are established by Borrower; (iii) purchase money security interests and
liens in connection with capital leases incurred in the ordinary course of
business (to the extent such liens are only on the leased property) or existing
on after acquired property at the time of its acquisition by the Borrower; (iv)
Liens existing on property as of the date of this Note; (v) Liens securing the
performance of bids, trade contracts, leases, surety bonds and the like; (vi)
leases and sublicenses granted to others in the ordinary course of business;
(vii) Liens consisting of rights of set-off or bankers liens of a customary
nature; (viii) Liens in connection with the establishment of receivable lines of
credit with commercial banks or other institutional lenders; (ix) Liens
consisting of agreements to refrain from giving or creating Liens (other than
the Lien and security interest granted to Lender hereunder) in connection with
joint venture agreements, strategic alliances and the like; (x) Liens granted in
all of the Company's assets pursuant to the secured Promissory Note dated July
30, 1999; (xi) Liens granted in all of the Company's assets pursuant to the
secured Promissory Note dated February 22, 2000; (xii) Liens granted in all of
the Company's assets pursuant to the secured Promissory Note dated April 14,
2000, as amended; and (xiii) Liens granted in all of the Company's assets
pursuant to the Secured Promissory Note dated December 29, 2000.

                "Trademarks" means any trademark and servicemark rights, whether
registered or not, applications to register and registrations of the same and
like protections, and the entire goodwill of the business of Borrower connected
with and symbolized by such trademarks.

                "UCC" means the Uniform Commercial Code in effect from time to
time in the relevant jurisdiction.

        2.      Governing Law; Venue. This Note shall be governed by the laws of
the State of California, without giving effect to conflicts of law principles.
Borrower and Lender agree that all actions or proceedings arising in connection
with this Note shall be tried and litigated only in the state courts located in
the County of Santa Clara, State of California, in the United States District
Court for the Northern District of California, or at Lender's option, any court
in which Lender determines it is necessary or appropriate to initiate legal or
equitable proceedings in order to exercise, preserve, protect or defend any of
its rights and remedies under this Note or otherwise or to exercise, preserve,
protect or defend its Lien, and the priority thereof, against the Collateral,
and which has subject matter jurisdiction over the matter in controversy.

        3.      Notices. Any notice or communication required or desired to be
served, given or delivered hereunder shall be in the form and manner specified
below, and shall be addressed to the party to be notified as follows:

                                      -9-
<PAGE>   10

               If to the Lender: Walter Bosch
                                 Fraumunsterstr. 9
                                 8001 Zurich
                                 Switzerland

               If to Borrower:   Euphonix, Inc.
                                 220 Portage Avenue
                                 Palo Alto, California 94306
                                 Attention: Steve Vining
                                 Fax: (650) 846-1131

               With a copy to:   Wilson Sonsini Goodrich & Rosati,
                                 Professional Corporation
                                 650 Page Mill Road
                                 Palo Alto, California  94304-1050
                                 Attn: John Roos, Esq.
                                 Fax: (650) 493-6811

or to such other address as each party designates to the other by notice in the
manner herein prescribed. Notice shall be deemed given hereunder if (i)
delivered personally or otherwise actually received, (ii) sent by overnight
delivery service, (iii) mailed by first-class United States mail, postage
prepaid, registered or certified, with return receipt requested, or (iv) sent
via telecopy machine with a duplicate signed copy sent on the same day as
provided in clause (ii) above. Notice mailed as provided in clause (iii) above
shall be effective upon the expiration of three (3) business days after its
deposit in the United States mail, and notice telecopied as provided in clause
(iv) above shall be effective upon receipt of such telecopy if the duplicate
signed copy is sent under clause (iv) above. Notice given in any other manner
described in this section shall be effective upon receipt by the addressee
thereof; provided, however, that if any notice is tendered to an addressee and
delivery thereof is refused by such addressee, such notice shall be effective
upon such tender unless expressly set forth in such notice.

        4.      Lender's Rights; Borrower Waivers. Lender's acceptance of
partial or delinquent payment from Borrower hereunder, or Lender's failure to
exercise any right hereunder, shall not constitute a waiver of any obligation of
Borrower hereunder, or any right of Lender hereunder, and shall not affect in
any way the right to require full performance at any time thereafter. Except as
otherwise expressly provided herein, Borrower waives presentment, diligence,
demand of payment, notice, protest and all other demands and notices in
connection with the delivery, acceptance, performance, default or enforcement of
this Note. In any action on this Note, Lender need not produce or file the
original of this Note, but need only file a photocopy of this Note certified by
Lender be a true and correct copy of this Note in all material respects.

        5.      Severability. Whenever possible each provision of this Note
shall be interpreted in such manner as to be effective and valid under
applicable law, but if any provision is prohibited by or invalid under
applicable law, it shall be ineffective to the extent of such prohibition or
invalidity, without invalidating the remainder of the provision or the remaining
provisions of this Note.

                                      -10-
<PAGE>   11

        6.      Amendment. This Note may not be amended or modified, nor may any
of its terms be waived, except by written instruments signed by Borrower and the
Lender.

        7.      Binding Effect. This Note shall be binding upon, and shall inure
to the benefit of, Borrower and the Lender hereof and their respective
successors and assigns; provided, however, that Borrower's rights and
obligations shall not be assigned or delegated without Lender's prior written
consent, given in its sole discretion, and any purported assignment or
delegation without such consent shall be void ab initio.

        8.      Headings. Section headings used in this Note have been set forth
herein for convenience of reference only. Unless the contrary is compelled by
the context, everything contained in each section hereof applies equally to this
entire Note.

        9.      No Usury. This Note is subject to the express condition that at
no time shall the Borrower be obligated or required to pay interest hereunder at
a rate which could subject Lender to either civil or criminal liability as a
result of being in excess of the maximum rate which the Borrower is permitted by
law to contract or agree to pay. If, by the terms of this Note, the Borrower is
at any time required or obligated to pay interest at a rate in excess of such
maximum rate, the rate of interest under this Note shall be deemed to be
immediately reduced to such maximum rate and interest payable hereunder shall be
computed at such maximum rate and the portion of all prior interest payments in
excess of such maximum rate shall be applied and shall be deemed to have been
payments in reduction of the principal balance of this Note.

        10.     Attorneys' Fees. Should any litigation, enforcement or
collection action be commenced between any of the parties to this Note under or
in connection with this Note, the prevailing party in such litigation,
enforcement or collection action shall be entitled, in addition to such other
relief as may be granted, to a reasonable sum as and for its attorneys' fees in
such litigation, enforcement or collection action which shall be determined by
the court in such litigation, enforcement or collection action or in a separate
action brought for that purpose. The provisions of this section shall survive
the entry of any judgment or award and shall continue to apply with respect to
any action to collect or recover any such judgment or award.

        11.     Counterparts. This Agreement may be executed in any number of
counterparts, each of which shall be an original, but all of which together
shall constitute one instrument.







                [remainder of the page intentionally left blank]

                                      -11-
<PAGE>   12

        IN WITNESS WHEREOF, the Borrower and the Lender have caused this Note to
be duly executed on the date first written above.



                                    EUPHONIX, INC.



                                    By:
                                       ------------------------------------
                                    Name:   Steve Vining
                                    Title:  Chief Executive Officer



                                    LENDER



                                    ---------------------------------------
                                    Walter Bosch





                   [SIGNATURE PAGE TO SECURED PROMISSORY NOTE]


<PAGE>   13


                                    EXHIBIT A

                        COLLATERAL DESCRIPTION ATTACHMENT
                           TO SECURED PROMISSORY NOTE

        All personal property of Borrower (herein referred to as "Borrower" or
"Debtor") whether presently existing or hereafter created, written, produced or
acquired, including, but not limited to:

        (1) all accounts receivable, accounts, chattel paper, contract rights
(including, without limitation, royalty agreements, license agreements and
distribution agreements), documents, instruments, money, deposit accounts and
general intangibles, including, without limitation, returns, repossessions,
books and records relating thereto, and equipment containing said books and
records, all investment property, including securities and securities
entitlements;

        (2) all software, computer source codes and other computer programs
(collectively, the "Software Products"), and all common law and statutory
copyrights and copyright registrations, applications for registration, now
existing or hereafter arising, United States of America and foreign, obtained or
to be obtained on or in connection with the Software Products, or any parts
thereof or any underlying or component elements of the Software Products
together with the right to copyright and all rights to renew or extend such
copyrights and the right (but not the obligation) of Lender (herein referred to
as "Lender" or "Secured Party") to sue in its own name and/or the name of the
Debtor for past, present and future infringements of copyright;

        (3) all goods, including, without limitation, equipment and inventory
(including, without limitation, all export inventory);

        (4) all guarantees and other security therefor;

        (5) all trademarks, service marks, trade names and service names and the
goodwill associated therewith including, without limitation, the following:

                      Reel Feel(TM)
                      Clear Displays(TM)
                      Track Panner(TM)
                      SnapShot Recall(TM)
                      DSC(TM) (Digital Studio Controller)
                      Hyper-Surround(TM)
                      Total Automation(TM)
                      Mixview(TM)

        (6) (a) all patents and patent applications filed in the United States
Patent and Trademark Office or any similar office of any foreign jurisdiction,
and interests under patent license agreements, including, without limitation,
the inventions and improvements described and claimed therein, (including,
without limitation, United States Patents Nos. 5524060, 5402501, 5399820,
5677959 and 6,057,829 and applications for United States patents for (i)
Multiple Driver Rotary Control for Audio Processors or Other Uses, (ii)
Functional Panel for Audio Mixer, and (iii) Plug-in Modules for

<PAGE>   14



Digital Signal Processor Functionalities), (b) licenses pertaining to any patent
whether Debtor is licensor or licensee, (c) all income, royalties, damages,
payments, accounts and accounts receivable now or hereafter due and/or payable
under and with respect thereto, including, without limitation, damages and
payments for past, present or future infringements thereof, (d) the right (but
not the obligation) to sue for past, present and future infringements thereof,
(e) all rights corresponding thereto throughout the world in all jurisdictions
in which such patents have been issued or applied for, and (f) the reissues,
divisions, continuations, renewals, extensions and continuations-in-part with
any of the foregoing (all of the foregoing patents and applications and
interests under patent license agreements, together with the items described in
clauses (a) through (f) in this paragraph are sometimes herein individually and
collectively referred to as the "Patents");

        (7) all rights in and to (i) the on-air mixing consoles of the Series
CS3000B, (ii) mixer hardware software designs, (iii) Real Time(TM) software
design, and (iv) analog and digital audio hardware design expertise; and

        (8) all products and proceeds, including, without limitation, insurance
proceeds, of any of the foregoing.

Notwithstanding the foregoing, the grant of a security interest as provided
herein shall not extend to, and the term "Collateral" shall not include, any
contractual, license or lease rights or interests in which Borrower is the
grantee, licensee or lessee thereunder to the extent that Borrower, whether by
law or by the terms of such contract, license or lease, is not permitted to
assign or grant a security in interest in its rights thereunder without the
consent of the other party thereto.


                                      -2-
<PAGE>   15


                                    EXHIBIT B

                          REGISTRATION RIGHTS AGREEMENT



<PAGE>   16






                                    EXHIBIT C

                              COMMON STOCK WARRANT