<PAGE>   1
                                                                   EXHIBIT 10.28

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 1s 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

Eight Hundred Thousand Dollars
($800,000.00)                                                     April 14, 2000


        FOR VALUE RECEIVED, the undersigned, Euphonix, Inc., a California
corporation ("Borrower"), hereby promises to pay to Dieter Meier and Walter
Bosch, each an individual, and Onset Ventures, a Delaware corporation
(individually an "Investor" and collectively, the "Investors" or "Lender"), or
registered assigns, the principal sum Eight Hundred Thousand Dollars ($800,000)
(the "Maximum Principal Amount") or so much of the Maximum Principal Amount as
may from time to time have been advanced by each Investor and be outstanding,
together with accrued interest, as provided herein, with the Maximum Principal
Amount hereof (or lesser amount, to the extent that less than the full amount of
the Maximum Principal Amount is advanced and outstanding) allocable among the
Investors as follows:


<TABLE>
<CAPTION>
    NAME OF INVESTOR             MAXIMUM PRINCIPAL AMOUNT        PRO RATA SHARE
    ----------------             ------------------------        --------------
<S>                              <C>                             <C>
      Dieter Meier                     $200,000.00                   25%
      Walter Bosch                     $200,000.00                   25%
      Onset Ventures                   $400,000.00                   50%
                                       -----------                   ---
                    Total              $800,000.00                  100.00%
</TABLE>

A.      Principal.

        1. Advances. From the date hereof until 5:00 p.m. Pacific Standard Time
on June 30, 2000, Borrower may from time to time request advances from Lender
(individually an "Advance" and collectively the "Advances") by giving written
notice to the Investors in accordance with the terms hereof, which notice shall
indicate the amount of the Advance requested; provided, however, that no advance
shall be in the aggregate less than $800,000. Subject to the satisfaction or
waiver of the conditions set forth in Section A.3 below, and provided that the
requested Advance would not

<PAGE>   2

cause an Event of Default (as defined in Section E below) to occur, Lender shall
make the Advance to Borrower within three (3) business days of receipt of
Borrower's notice for each Advance. Lender shall not be obligated to make an
Advance to the extent that such Advance, when aggregated with all prior
Advances, would exceed the then-existing Maximum Principal Amount.

        2. Commitments. Each Investor shall advance to Borrower its Pro Rata
Share of each Advance based on its proportionate share of the Maximum Principal
Amount set forth above besides its name. Each Investor shall be severally but
not jointly liable to make its Pro Rata Share of the Advances hereunder. Failure
by any Investor to fund its Pro Rata Share of any Advance shall not relieve any
other Investor from its obligation to fund its Pro Rata Share thereof.

        3. Conditions to Advances. Borrower's right to request, and Lender's
obligation to make, each Advance shall be subject, in each case, to the
satisfaction of the following conditions, any or all of which may be waived by
Lender, in its sole and exclusive discretion, to the extent permitted by law:

            (a) The representations and warranties contained in Section D.2 and
D.3 shall be true and correct in all material respects on and as of the date of
such request for an Advance and on the effective date of each Advance as though
made at and as of each such date, and no Event of Default shall have occurred
and be continuing, or would result from such Advance.

            (b) There shall be no law, order, rule or regulation of any
governmental authority in effect which has the effect of prohibiting, making
unlawful or hindering any of the transactions contemplated by this Note.

            (c) There shall be no outstanding Event of Default and no condition
which, with notice or passage of time or both would constitute an Event of
Default.

            (d) The Board of Directors of Borrower shall have approved this Note
and the transactions evidence by this Note, including without limiting the
conversion feature of this Note.

            (e) Certain shareholders of Borrower shall have signed and delivered
to Lender a written agreement in a form acceptable to Lender evidencing their
agreement to vote their shares of common stock of Borrower in favor of the
approval of the convertibility of this Note as set forth below.

        4. Use of Proceeds. The proceeds of Advances shall be used for general
corporate purposes, including for working capital. The proceeds of Advances
shall not be used for payments or distributions to shareholders, directors,
officers or affiliates of the Borrower, Notwithstanding the foregoing, such
proceeds may be used for payment of salaries and accrued bonuses of officers and
employees of the Borrower.

B. Interest. Interest shall accrue with respect to Advances on the principal sum
hereunder at the per annum rate of ten percent (10.00%), 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 C below) upon
payment or conversion of the principal sum of this Note pursuant to Section C
below.

                                                                             -2-
<PAGE>   3

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 Advances on the principal sum hereunder at the per annum rate of
fourteen percent (14.00%), net of any deductions or withholding taxes.

C.      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 January 1, 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 any necessary shareholder, regulatory and other approvals or
consents for the convertibility of this Note as set forth below are necessary
but not obtained by June 30, 2000, (i) the outstanding principal sum from all
Advances as of the date thereof and all future Advances from the date thereof
and (ii) accrued interest thereon, shall be repaid in full upon demand by the
Investors representing two-thirds (2/3) of the then outstanding principal sum of
this Note; provided, however, no such demand may be made until January 1, 2001;
and provided, further, that the Investors must provide at least one (1) month
prior written notice to the Borrower prior to such demand. To the extent the
approvals or consents contemplated herein are obtained after June 30, 2000, this
Note shall not be subject to repayment upon demand as set forth herein but
rather in accordance with the scheduled payment as set forth in Section C.1
above. 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 Investors
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 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 any necessary shareholders, regulatory and
other approvals or consents and further subject to Section C.5 (c) hereof, all
or part of the principal sum of this Note, together with the accrued interest
thereon (including any principal amounts which have not been advanced under this
Note), 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 (including any
principal amounts which have not been advanced under this Note) plus accrued
interest thereon by (ii) the stock price of the Common Stock

                                                                             -3-
<PAGE>   4

as traded on the Nasdaq Stock Market on the day of execution of this Note which
is $3 5/8 per share. In the event that Investors (or either of them) exercise
this conversion right and the full amount of principal under this Note has not
been advanced, then as part of such conversion, such Investor(s) shall pay to
Borrower such Investor's unadvanced portion of the principal amount of this
Note.

            (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 each Investor, at
its principal office, or other address notified by each Investor to the Borrower
from time to time, a certificate or certificates for the number of shares
(representing its pro rata portion) to which the Investor 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
each Investor 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 Investor exercising its rights under Section 5
hereunder at the time of such exercise.

            (c) Notwithstanding anything herein to the contrary, Section C.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
Investors fourteen (14) calendar days prior to the consummation of any such
Transaction and, notwithstanding anything to the contrary contained elsewhere in
this Note, Investors may exercise their rights of conversion during such 14-day
period.

D.      Security Interest.

        1. Grant of Security Interest. Upon the first Advance hereunder,
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, accrued
interest, other advances made under this Note and any attorneys' fees to which
Lender is entitled under this Note. The amounts payable under this Note and the
security interest granted hereunder shall be senior in right to payment and lien
priority to the rights and security interest granted to the holders of the
Secured Promissory Note dated February 22, 2000 in the original principal amount
of $1,500,000 (the "February 22, 2000 Note"), subject to the consent of such
holders as provided in Section G below.

                                                                             -4-
<PAGE>   5

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

            (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.


                                                                             -5-
<PAGE>   6

            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 contemplate under Section C, 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 C which requires shareholder approval pursuant to the Nasdaq Stock
Market's shareholder approval provisions is obtained.

            (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

                                      -6-
<PAGE>   7

filing of financing statements and the filing of notices of security interests
with the United States Patent and Trademark Office.

E.      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; or

            (b) 60 days' lapse 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.

            (d) The occurrence of any default under the July 30, 1999 Note which
is not remedied within any applicable grace period provided therein.

        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 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

                                                                             -7-
<PAGE>   8

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 ether 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) The rights of Lender under this Note with respect to any
Collateral and the enforcement of the security interests and associated rights
hereunder may be exercised jointly by Investors or singly by any Investor
representing two-thirds (2/3) of the then outstanding principal sum of this
Note.

            (e) Upon the occurrence of an Event of Default, either Investor may
bring suit against Borrower to collect amounts due such Investor under this
Note.

            (f) Either Investor may bring suit against Borrower to enforce the
provisions of this Note.

F.      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:

                                                                             -8-
<PAGE>   9

  "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 1s 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.

            (c) Each Investor, 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.

            (d) Each Investor, by acceptance hereof, represents that it 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.

            (e) 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.

G.      Covenants.

        1. Subordination. Borrower shall use commercially reasonable efforts to
obtain the consent of the holders of the February 22, 2000 Note and the July 30,
1999 Note to the subordination of the right to payment under and the security
interest granted pursuant to such promissory note as described in Section D.1
above. Failure to obtain such consent by June 30, 2000 shall constitute an Event
of Default hereunder. Notwithstanding anything to the contrary contained
elsewhere in this Note, Lender shall not be required to make any advances under
this Note unless and until such consent is obtained and delivered to Lender.

                                                                             -9-
<PAGE>   10

H.      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 e;<tensions 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.

            "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.

                                                                            -10-
<PAGE>   11

            "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; and (x) liens
granted in all of the Company's assets pursuant to the secured Promissory Note
dated July 30, 1999.

            "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 and federal courts
located in the City and County of San Francisco, State 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. Borrower waives any right it may have to assert the
doctrine of forum non conveniens or to object to such venue, and consents to any
court ordered relief Borrower waives personal service of process and agrees that
a summons and complaint commencing an action or proceeding in any such court
shall be promptly served and shall confer personal jurisdiction if served by
registered or certified mail to Borrower. The choice of forum set forth herein
shall not be deemed to preclude the enforcement of any judgment obtained in such
forum, or the taking of any action under this Note to enforce the same, in any
appropriate jurisdiction.

        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:

                                                                            -11-
<PAGE>   12

                      If to Investors:      Dieter Meier

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


                                            Walter Bosch

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


                                            Onset Ventures

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

                      With a copy to:
                                            ------------------------------------
                                            ------------------------------------
                                            ------------------------------------
                                            ------------------------------------
                                            ------------------------------------
                                            ------------------------------------


                      and to:
                                            ------------------------------------
                                            ------------------------------------
                                            ------------------------------------
                                            ------------------------------------
                                            ------------------------------------
                                            ------------------------------------


                      If to Borrower:       Euphonix, Inc.
                                            220 Portage Avenue
                                            Palo Alto, California 94306
                                            Attn: Barry Margerum
                                            Fax: (650) 846-l131


                      With a copy to:       Wilson Sonsini Goodrich & Rosati
                                            Professional Corporation
                                            650 Page Mill Road
                                            Palo Alto, California 94304-l050
                                            Attn: John Roos, Esq.
                                            Fax:   (650) 493-6811


                                                                            -12-
<PAGE>   13

            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.

        6. Amendment Provisions. Except for increases in the Maximum Principal
Amount of this Note as provided herein, this Note may not be amended or
modified, nor may any of its terms be waived, except by written instruments
signed by Borrower and Lender.

        7. Binding Effect. This Note shall be binding upon, and shall inure to
the benefit of, Borrower and the holder 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. Time of Essence. Time is of the essence of each and every provision
of this Note.

        9. 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.

        10. 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

                                                                            -13-
<PAGE>   14

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.

        11. 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 shah survive the
entry of any judgement or award and shall continue to apply with respect to any
action to collect or recover any such judgment or award.


                                                                            -14-
<PAGE>   15

        IN WITNESS WHEREOF, the Borrower and each of the Investors has caused
this Note to be duly executed on the date first written above.


                                            EUPHONIX, INC.


                                            By:
                                                     ---------------------------
                                            Name:    Barry Margerum
                                            Title:   Chief Executive Officer



                                            "INVESTORS"



                                            ------------------------------------
                                            Dieter Meier



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



                                            Onset Ventures



                                            ------------------------------------
                                            By:
                                            Title:   General Partner


<PAGE>   16

                                   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 and
5677959
<PAGE>   17

and applications for United States patents for (i) Computer-Mirrored Panel Input
Devices, (ii) Multiple Driver Rotary Control for Audio Processors or Other Uses,
(iii) Functional Panel for Audio Mixer, and (iv) Cont. and Amendment of
"Computer-Mirrored Panel Input Devices"), (b) licenses pertaining to any patent
whether Debtor is licenser 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-