Document:

<PAGE>

                                                                     EXHIBIT 4.6

                         Quantum Effect Devices, Inc.
                  1999 Employee Stock Purchase Plan ("ESPP")
                            Enrollment/Change Form

<TABLE>
<CAPTION>
                       Action                                              Complete Sections:
                       ------                                              -----------------
<S>                 <C>                                                    <C>
---------------     ----
SECTION 1:               New Enrollment                                    2, 3, 6, 7
---------------     ----
ACTIONS                  Payroll Deduction Change                          2, 4, 7
                    ----
                         Withdrawal                                        2, 5, 7
                    ----
                         Beneficiary Change (optional)                     2, 6, 7
                    ----
================================================================================================================
---------------
SECTION 2:
---------------
EMPLOYEE            Name____________________________________________________________________________
DATA                         Last                           First                    MI

                    Home Address____________________________________________________________________
                                                            Street

                    ________________________________________________________________________________
                             City                           State                    Zip Code

                    Social Security #: ________________--_______________--_______________

================================================================================================================
---------------
SECTION 3:
---------------
NEW                 Effective:                           Payroll Deduction Amount:  _____% of Earnings
ENROLLMENT          [_]  _______________                 (whole percentage, maximum 10%)

                    [_]  Initial Offering

================================================================================================================
---------------
SECTION 4:
---------------
PAYROLL             Effective _____________________,  I authorize the following new level of payroll
DEDUCTION           deduction: _____% of Earnings (whole percentage, maximum 10%).
CHANGE
                    NOTE:     You may decrease (but not increase) your rate of payroll deductions, including
                    ----              --------
                              to zero, once (and only once) during a Purchase Period. However, you may change
                              your rate of payroll deductions (either an increase or a decrease) effective
                              either as of the first day of the next Purchase Period of the ongoing Offering
                              or the first day of the next Offering. To withdraw entirely from the ongoing
                              Offering and receive a refund of your payroll deductions, complete Section 5.

================================================================================================================
---------------
SECTION 5:
---------------
WITHDRAWAL          Effective with the pay period beginning __________________, I withdraw from the ESPP.

                    NOTE:     Your election to withdraw from the ongoing Offering cannot be changed, and you
                    ----
                              may not resume participation in the ESPP prior to the commencement of the next
                              Offering. In connection with your withdrawal, your payroll deductions will be
                              refunded to you as soon as practicable, without interest.

                    NOTE:     If your employment terminates for any reason, you will automatically be withdrawn
                    ----
                              from the ESPP, and any payroll deductions collected and not previously used to
                              purchase stock will automatically be refunded to you as soon as practicable.

================================================================================================================
---------------
SECTION 6:          Beneficiary                                  Relationship of Beneficiary
---------------     -----------                                  ---------------------------

BENEFICIARY
DESIGNATION         ______________________________________       _____________________________________________
(Optional)

================================================================================================================
---------------
SECTION 7:
---------------
AUTHORIZATION

I hereby authorize Quantum Effect Devices, Inc. to enroll me in the ESPP, to make regular deductions in the
amount indicated above, and to purchase shares for me. If I have elected to withdraw from the ESPP, I
authorize Quantum Effect Devices, Inc. to distribute my accumulated deductions to me. Any authorization for
payroll deductions will continue until canceled or changed by me in accordance with the terms of the ESPP.
Deductions will cease upon the termination of my status as an Employee, termination of the ESPP or upon my
election to withdraw from the ESPP. I agree to be bound by the terms and provisions of the ESPP, as described
in the official text of the ESPP, and any applicable offering document.

Date: _____________________        Signature: ________________________________________________________________
</TABLE>
<PAGE>

                         Quantum Effect Devices, Inc.
                       1999 Employee Stock Purchase Plan
                                   Offering

                           Adopted September 1, 1999
                           Amended January 11, 2000

1.   Grant of Rights.

     (a)  The Board of Directors ("Board") of Quantum Effect Devices, Inc., a
Delaware corporation (the "Company"), pursuant to the Company's 1999 Employee
Stock Purchase Plan (the "Plan"), hereby authorizes the grant of Rights to
purchase Shares of the Company to all Eligible Employees (an "Offering").
Defined terms not explicitly defined in this Offering but defined in the Plan
shall have the same definitions as in the Plan.  In the event of any conflict
between the provisions of an Offering and those of the Plan (including
interpretations, amendments, rules and regulations that may from time to time be
promulgated and adopted pursuant to the Plan), the provisions of the Plan shall
control.

     (b)  An "Offering Date" is the first day of an Offering. An Offering may
consist of one purchase period or may be divided into shorter purchase periods
("Purchase Periods"). A "Purchase Date" is the last day of a Purchase Period or
the Offering, as the case may be.

     (c)  The first Offering shall begin on the effective date of the initial
public offering of the Shares and end on February 14, 2002 (the "Initial
Offering"). The Initial Offering will be divided into four (4) shorter Purchase
Periods of approximately six (6) months in duration, with the initial Purchase
Period ending on August 14, 2000, the second Purchase Period ending on February
14, 2001, the third Purchase Period ending on August 14, 2001 and the fourth
Purchase Period ending on February 14, 2002.

     (d)  Except as otherwise provided, each Offering hereunder shall be twenty-
four (24) months long and shall be divided into four (4) shorter Purchase Period
approximately six (6) months in length. Offerings shall be concurrent. A new
Offering shall start every six (6) months.

     (e)  Commencing on August 15, 2000, a new 24-month Offering shall begin
every August 15 and February 15. Each such Offering shall end on the day prior
to the second anniversary of its Offering Date unless sooner terminated as
provided above.

     (f)  An Eligible Employee may enroll in only one Offering at a time.

     (g)  If on the first day of any Purchase Period during an Offering (i.e.,
August 15 or February 15) the fair market value of the Shares is less than it
was on the Offering Date for that

                                       1
<PAGE>

Offering, then the Offering shall immediately terminate, and the employees who
were enrolled in the terminated Offering shall automatically be enrolled in the
new Offering that starts that day.

     (h)  Prior to the commencement of any Offering, the Board may change any or
all terms of such Offering and any subsequent Offerings. The granting of Rights
pursuant to each Offering hereunder shall occur on each respective Offering Date
unless, prior to such date (i) the Board (or such Committee) determines that
such Offering shall not occur, or (ii) no Shares remain available for issuance
under the Plan in connection with the Offering.

     (i)  Notwithstanding any other provisions of an Offering, if the terms of
an Offering as previously established by the Board would, as a result of a
change to applicable accounting standards, generate a charge to earnings, such
Offering shall terminate effective as of the day prior to the date such change
to accounting standards would otherwise first apply to the Offering (the
"Offering Termination Date"), and such Offering Termination Date shall be the
final Purchase Date of such Offering. A subsequent Offering shall commence on
such date and on such terms as shall be provided by the Board.

2.   Eligible Employees.

     (a)  All employees of the Company and each of its Affiliates incorporated
in the United States shall be granted Rights to purchase Shares under each
Offering on the Offering Date of such Offering, provided that each such employee
otherwise meets the employment requirements of subparagraph 6(a) of the Plan and
has been continuously employed for at least five (5) days on the Offering Date
of such Offering (an "Eligible Employee"); however, the five-day eligibility
requirement shall be waived with respect to the Initial Offering only.

     (b)  Notwithstanding the foregoing, the following employees shall not be
Eligible Employees or be granted Rights under an Offering: (i) part-time or
seasonal employees whose customary employment is less than twenty (20) hours per
week or five (5) months per calendar year or (ii) 5% stockholders (including
ownership through unexercised options) described in subparagraph 6(c) of the
Plan.

3.   Rights.

     (a)  Subject to the limitations contained herein and in the Plan, on each
Offering Date each Eligible Employee shall be granted the Right to purchase the
number of Shares purchasable with up to ten percent (10%) of such Eligible
Employee's Earnings paid during such Offering after the Eligible Employee first
commences participation; provided, however, that no employee may purchase Shares
on a particular Purchase Date that would result in more than ten percent (10%)
of such employee's Earnings in the period from the Offering Date to such
Purchase Date having been applied to purchase Shares under all ongoing Offerings
under the Plan and all other Company plans intended to qualify as "employee
stock purchase plans" under Section 423 of the Internal Revenue Code of 1986, as
amended (the "Code").

     (b)  For this Offering, "Earnings" means the total compensation paid to an
employee, including all salary, wages (including amounts elected to be deferred
by the employee, that

                                       2
<PAGE>

would otherwise have been paid, under any cash or deferred arrangement
established by the Company), overtime pay, commissions, bonuses, and other
remuneration paid directly to the employee, but excluding profit sharing, the
cost of employee benefits paid for by the Company, education or tuition
reimbursements, imputed income arising under any Company group insurance or
benefit program, traveling expenses, business and moving expense reimbursements,
income received in connection with stock options, contributions made by the
Company under any employee benefit plan, and similar items of compensation.

     (c)  Notwithstanding the foregoing, the maximum number of Shares an
Eligible Employee may purchase on any Purchase Date in an Offering shall be such
number of Shares as has a fair market value (determined as of the Offering Date
for such Offering) equal to (x) $25,000 multiplied by the number of calendar
years in which the Right under such Offering has been outstanding at any time,
minus (y) the fair market value of any other Shares (determined as of the
relevant Offering Date with respect to such Shares) which, for purposes of the
limitation of Section 423(b)(8) of the Code, are attributed to any of such
calendar years in which the Right is outstanding. The amount in clause (y) of
the previous sentence shall be determined in accordance with regulations
applicable under Section 423(b)(8) of the Code based on (i) the number of Shares
previously purchased with respect to such calendar years pursuant to such
Offering or any other Offering under the Plan, or pursuant to any other Company
plans intended to qualify as "employee stock purchase plans" under Section 423
of the Code, and (ii) the number of Shares subject to other Rights outstanding
on the Offering Date for such Offering pursuant to the Plan or any other such
Company plan.

     (d)  The maximum aggregate number of Shares available to be purchased by
all Eligible Employees under an Offering shall be the number of Shares remaining
available under the Plan on the Offering Date. If the aggregate purchase of
Shares upon exercise of Rights granted under the Offering would exceed the
maximum aggregate number of Shares available, the Board shall make a pro rata
allocation of the Shares available in a uniform and equitable manner.

4.   Purchase Price.

     (a)  The purchase price of the Shares under the Offering shall be the
lesser of eighty-five percent (85%) of the fair market value of the Shares on
the Offering Date or eighty-five percent (85%) of the fair market value of the
Shares on the Purchase Date, in each case rounded up to the nearest whole cent
per Share.

     (b)  For the Initial Offering, the fair market value of the Shares at the
time when the Offering commences shall be the price per Share at which Shares
are first sold to the public in the Company's initial public offering as
specified in the final prospectus with respect to that offering.

                                       3
<PAGE>

5.   Participation.

     (a)  An Employee who is an Eligible Employee at the beginning of an
Offering may elect to participate in such Offering at the beginning of the
Offering or at the start of any new Purchase Period during the Offering.

     (b)  A Participant who is enrolled in an Offering automatically will be
enrolled in the next Offering that commences after the current Offering ends.

     (c)  An Eligible Employee shall become a Participant in an Offering by
delivering an agreement authorizing payroll deductions.  Such deductions must be
in whole percentages, with a minimum percentage of one percent (1%) and a
maximum percentage of ten percent (10%) of Earnings.  A Participant may not make
additional payments into his or her account.  The agreement shall be made on
such enrollment form as the Company provides, and must be delivered to the
Company at least five (5) days before the Offering Date, or before such later
date specified in subparagraph 5(a), in advance of the date of participation to
be effective, unless a later time for filing the enrollment form is set by the
Board for all Eligible Employees with respect to a given Offering Date.  For the
Initial Offering, the time for filing an enrollment form and commencing
participation for individuals who are Eligible Employees on the Offering Date
for the Initial Offering may be after the Offering Date, as determined by the
Company and communicated to such Eligible Employees.

     (d)  If the agreement authorizing payroll deductions is required to be
delivered to the Company or designated Affiliate a specified number of days
before the Offering Date to be effective, then an employee who becomes eligible
during the required delivery period shall not be considered to be an Eligible
Employee at the beginning of the Offering.

6.   Changing Participation Level during Offering; Withdrawal from Offering.

     (a)  A Participant may not increase his or her deductions during the course
of a Purchase Period. A Participant may increase or decrease his or her
deductions prior to the beginning of a new Purchase Period or a new Offering, to
be effective at the beginning of such new Purchase Period or new Offering. A
Participant shall make a change in his or her participation level by delivering
a notice to the Company in such form and at such time as the Company provides.

     (b)  A Participant may reduce (including to zero) his or her deductions
once (and only once) during a Purchase Period, effective as soon as
administratively practicable. A Participant shall make a change in his or her
participation level by delivering a notice to the Company in such form and at
such time as the Company provides.

     (c)  Except as otherwise specifically provided herein, a Participant may
not increase or decrease his or her participation level during the course of an
Offering.

                                       4
<PAGE>

     (d)  Notwithstanding the foregoing, a Participant may withdraw from an
Offering and receive his or her accumulated payroll deductions from the Offering
(reduced to the extent, if any, such deductions have been used to acquire Shares
for the Participant on any prior Purchase Dates), without interest, or reduce
his or her participation percentage to zero (0), at any time prior to the end of
the Offering, excluding only each five (5) business day period immediately
preceding a Purchase Date (or such shorter period of time determined by the
Company and communicated to Participants) by delivering a withdrawal notice to
the Company in such form as the Company provides.

7.   Purchases.

     Subject to the limitations contained herein, on each Purchase Date, each
Participant's accumulated payroll deductions (without any increase for interest)
shall be applied to the purchase of whole Shares, up to the maximum number of
Shares permitted under the Plan and the Offering.

8.   Notices and Agreements.

     Any notices or agreements provided for in an Offering or the Plan shall be
given in writing, in a form provided by the Company, and unless specifically
provided for in the Plan or this Offering shall be deemed effectively given upon
receipt or, in the case of notices and agreements delivered by the Company, five
(5) days after deposit in the United States mail, postage prepaid.

9.   Exercise Contingent on Stockholder Approval.

     The Rights granted under an Offering are subject to the approval of the
Plan by the Shareholders as required for the Plan to obtain treatment as a tax-
qualified employee stock purchase plan under Section 423 of the Code.

10.  Offering Subject to Plan.

     Each Offering is subject to all the provisions of the Plan, and its
provisions are hereby made a part of the Offering, and is further subject to all
interpretations, amendments, rules and regulations which may from time to time
be promulgated and adopted pursuant to the Plan.

                                       5<PAGE>

                                                                   EXHIBIT 10.16

                       FIRST ADDENDUM TO LEASE AGREEMENT

BETWEEN:  SOCIETE EN COMMANDITE DUKE-WELLINGTON, a limited partnership duly
          constituted by virtue of the Civil Code of Quebec, having its head
          office at 255 St. Jacques Street, 1st floor, Montreal, Province of
          Quebec, H2Y lM6, acting and represented by its general partner, 9072-
          3552 Quebec Inc., itself acting and represented by Mr. Pierre-Luc
          Dumas and Mr. Andre Girard, duly authorized for the purposes of this
          agreement, as they so hereby declare;

                                               (hereinafter called the "Lessor")

AND:      NUANCE COMMUNICATIONS LIMITED, a legal person legally constituted by
          virtue of the Companies Act of Nova Scotia, having its head office at
          1959 Upper Water Street, Suite 800, Halifax, Nova Scotia B3J 3N2,
          acting and represented herein by Graham Smith, Vice-President and
          C.F.O., duly authorized for the purposes of this agreement, as he so
          hereby declares;

                                               (hereinafter called the "Lessee")

AND:      NUANCE COMMUNICATIONS, a company legally constituted by virtue of the
          laws of California, having its head office at 1380 Willow Road, Menlo
          Park, California 90425 USA, acting and represented herein by Graham
          Smith, Vice-President and C.F.O., duly authorized for the purposes of
          this agreement, as he so hereby declares;

                                                (hereinafter called the "Surety)

UNDERSTOOD THAT under the terms of a Lease Agreement signed on December 6/th/,
1999, (the "Lease") between the Lessor and the Lessee, the Lessor rented to the
Lessee, premises having an approximate area of twelve thousand square feet
(12,000 sq.ft.) located on the fourth (4/th/) floor ("Lease Premises") of the
building at 111, Duke Street, Montreal (Quebec) known as being Phase IV of La
Cite du Multimedia, situated on the emplacement described in Appendix "1"
hereof, for a term of seven (7) years and three (3) months beginning on the
latest of the following dates: i) August 1/st/ 2000, as defined in the Lease,
("Delivery Date") or ii) on a subsequent date if the Immovable's Basic
Facilities are completed after the Delivery Date.

UNDERSTOOD THAT the Lessee wishes to expand the rented surface of the Lease
Premises by approximately twenty two thousand square feet (22,000 sq.ft.) (the
"Additional Surface");

UNDERSTOOD THAT the Lessor agrees to rent to the Lessee the Additional Surface
as per the conditions hereafter detailed:

CONSEQUENTLY, IN COMPENSATION OF THE MUTUAL COMMITMENTS TO THIS AGREEMENT AND TO
THE LEASE, THE PARTIES AGREE TO THE FOLLOWING:
<PAGE>

1.  The preamble is an integral part of this addendum as if it was fully stated.

2.   The Lessor agrees to lease to the Lessee, who accepts same, the Additional
     Surface of which approximately five thousand square feet (5,000 sq.ft.) are
     located on the fourth (4/th/) floor and approximately seventeen thousand
     square feet (17,000 sq.ft.) are located on the second (2/nd/) floor.

3.   The terms and conditions of the Lease, as hereinafter modified, apply
     entirely to the Additional Surface.

4.   The following modifications to the Lease shall be made to reflect the lease
     of the Additional Surface:

     4.1  Article 1.1.1 Article 1.1.1 of the Lease is replaced by the following:
          -------------

     LEASE PREMISES: means premises having an approximate area of thirty four
     thousand square feet (34,000 sq.ft.) ("Leasable Area of the Lease
     Premises"), which shall be located on the 2/nd/ and the 4/th/ floors
     ("Lease Premises") of the building located at 111, Duke Street, Montreal
     (Quebec) ("Building"), as outlined in red in Appendix "D" included.

     4.2  Article 1.1.6 Article 1.1.6 of the Lease is replaced by the following:
          -------------

     SHARE:  The ratio between the Leasable Area of the Lease Premises and
     the leasable area of the Building, this ratio is currently stipulated
     by the parties to be nine point five per cent (9.5%); this percentage
     may vary, in the event of an increase or a decrease in the Leasable
     Area of the Lease Premises or the leasable area of the Building.

     4.3  Article 2.10 Article 2.10 of the Lease is modified by adding the
          ------------
          following sentence at the end of the paragraph:

     It is understood that if the Lessor elects to relocate the Lease
     Premises, such relocation shall include the whole of the Lease
     Premises and not a portion thereof.

     4.4  Article 26.1  Article 26.1 of the Lease is replaced by the following:
          ------------

     Parking:  The Lessor agrees to make available to the Lessee a number
     of parking spaces that shall not exceed the number obtained by
     calculating the ratio between the Leasable Area of the Lease Premises
     to one thousand five hundred square feet (1,500 sq.ft.), it being
     understood that the result shall be rounded down to the lower number.
     These twenty two (22) parking spaces (unreserved) will be located in
     the parking facilities that are part of the Immovable or adjacent to
     it, provided that the Lessee signs with the Lessor or with any third
     party to whom the Lessor may have assigned the operations of said
     parking facilities the model lease in force on occasion regarding
     these parking spaces and pay to the Lessor or to this third party,
     whichever is applicable, the rent in force on occasion for said
     parking spaces.  In the eventuality
<PAGE>

     where the Lessee rents additional spaces, the Lessor agrees to make
     available to the Lessee the same proportion of parking spots as that which
     is set out above to distribute the number of parking spots.

     4.5  Appendix As The amount of the surety, as stated in Appendix "A" of the
          -----------
          Lease, has been modified. The other terms and conditions of Appendix
          "A" of the Lease remain unchanged. The amount of the new letter of
          credit is four hundred forty five thousand dollars (445 000 $).
<PAGE>

IN WITNESS WHEREOF, the Lessee signed on this 9/th/ day of August 2000.

                                    NUANCE COMMUNICATIONS LIMITED

_______________________             By: ______________________________
Witness                                 Graham Smith

_______________________
Witness

IN WITNESS WHEREOF, the Surety signed on this 9/th/ day of August 2000.

                                    NUANCE COMMUNICATIONS

______________________________      By: ______________________________
Witness                                 Graham Smith

______________________________
Witness

IN WITNESS WHEREOF, the Lessor signed on this ____ day of _____________ 2000.

                                    SOCIETE EN COMMANDITE DUKE-WELLINGTON,
                                    acting by its general partner 9072-3552
                                    Quebec Inc.

______________________________      By: ______________________________
Witness                                 Pierre-Luc Dumas

______________________________      By: ______________________________
Witness                                 Andre Girard
<PAGE>

                                APPENDIX " 1 "

                       FIRST ADDENDUM TO LEASE AGREEMENT

                    CADASTRAL DESCRIPTION OF THE IMMOVABLE

Lot ONE MILLION EIGHT HUNDRED FOURTEEN THOUSAND FIVE HUNDRED SIXTY TWO (1814562)
of the Cadastre of Quebec.

Source: [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00014-of-00352.parquet"}, [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00014-of-00352.parquet"}]]