e002028.pdf

GENERAL INTEREST

parameter box for

MIDI software

convenient software synthesizer operation

Using a key-

board and

mouse to

operate the

innumerable

knobs and slid-

ers of a PC mix-

ing board can turn

playing around with a

sound synthesizer

into an agonizing

experience. With the

MIDI parameter box

it’s a different story!

Almost every PC these days has a

sound card. However, most PC users

employ it only to reproduce operating

system sounds, music from audio CDs

and sound effects for games and pre-

sentations. They thus use only the

standard features of the software for

the sound card, even though there are

outstanding programs available that

allow even non-musicians to exploit

the manifold features of modern

sound cards. These are sound synthe-

sizer programs.

Such synthesizers are sometimes

even included in the software pack-

ages that come with the better quality

sound cards. However, there are also

separate programs, such as Generator

from Native Instrument s or Rebirth

from Propellerhead. These programs

simulate the functions and operations

of a real synthesizer using a screen full

of sliders and knobs that are controlled

by the mouse. They represent a sort of

Gordian knot for anyone who wants to

do more than adjust a single slider.

The circuit described in this article

makes working with a software syn-

thesizer considerably easier. It utilises

the ability of a software synthesizer to

receive MIDI codes and to use these

codes to drive certain controllers. The

hardware of the MIDI parameter box

can thus be kept very simple. A micro-

controller reads the positions of eight

standard potentiometers in turn, via an

8-channel A/D converter. If one or more

of the potentiometer positions is

changed, the microcontroller sends this

information in MIDI format to the

MIDI input of the sound card. The soft-

ware synthesizer translates the MIDI

codes into new settings for the con-

troller in question.

Design by T. Klose

L AYERS

AND SUPER - LAYERS

The somewhat nebulous term ‘layer ’

often crops up in connection with

MIDI. Layers are actually nothing more

than groups of eight synthesizer func-

tions, which correspond to the eight

potentiometers of the MIDI parameter

box using a sort of multiple allocation.

Elektor Electronics

2/2000

470 Ω

C14

C10

D 1

100n

10µ

63V

INIT

VALUE

MCLR

RB0

RB1

RB2

RB3

RB4

RB5

RB6

RB7

SHDN

DOUT

RA0

RA1

RA2

RA3

IC2

IC1

CH0

CH1

CH2

CH3

CH4

CH5

CH6

CH7

SSTRB

DIN

PIC16F84

SCLK

RA4

-10/P

MAX186

K10

OSC1

OSC2

VREF

REFADJ

AGND

VSS

DGND

C7 C6 C5 C4 C3 C2 C1

C11

C12

C13

C15

C16

100n

10µ

63V

33p

10MHz

33p

8x 100n

IC3

1N4001

D 2

12V

7805

S9 ... S12

MIDI

DATA

BC547B

C17

C18

C19

1234

10µ

63V

100n

10µ

63V

MIDI CHANNEL

K10

P1...P8 = 8x 47k

+5V

see text

* zie tekst

* siehe Text

* voir texte

MEMORY RESET

LAYER

990087 - 11

Figure 1. The microcontroller reads the

status of the switches and of each of

the eight potentiometers in turn.

The parameter box has pushbutton

switches that can select one of six lay-

ers. The MIDI codes sent by each

potentiometer (or the controller) thus

vary according to the layer that is

selected.

The assignment of layers to specific

functions is not the same for all con-

trollers. Instead, controllers can be

divided into different groups. The var-

ious types of assignments are referred

to as super-layers. The MIDI parame-

ter box knows the three most com-

monly used groups and adapts the

MIDI codes to their specific needs.

Table 1 summarises the contents of the

six layers within the three super-layers.

number of Elektor projects, has an

interface to the microcontroller (IC2).

This interface carries the output data

from the D/A converter (DOUT) and

the clock (SCLK), as well as the settings

for the multiplexer (DIN). The con-

verter is controlled via the SSRB and

CS leads, synchronous to SCLK.

The microcontroller is a type

PIC16F84 IC that is clocked at 10 MHz.

In addition to the potentiometer posi-

tions, it also reads the layer selection

switches (S1–S6), the MIDI channel

switches ((S9–S12) and two other push-

button switches, MEMO and RESET.

Table 2 describes the meanings and

uses of all of the switches.

MIDI communication with the

sound card takes place via port lead

RB7. The MIDI signal can be visually

checked via the (blinking) LED D2.

There is a good reason why two con-

nection options are shown in the

drawing. Actually, the MIDI parameter

box should only be connected to the

sound card via a true, optically isolated

MIDI interface. Such an interface is

resistor in the data line pro-

tects against short circuits if this alter-

native is used. This type of connection

has one advantage, which is that the

operating power can be drawn from

the joystick port, so that D3, C17, C18

and IC3 are not needed.

This brings us to the power supply.

An external power supply is obligatory

with ‘real’ MIDI interfaces, in order to

ensure the electrical isolation of the PC

and the MIDI equipment. Only capac-

itors C17 through C19 and the voltage

regulator IC3 are needed to provide a

sufficiently stable +5 V. Power can be

Ω

H ARDWARE

The most important elements of the

hardware, which have already been

mentioned, can easily be recognised in

the schematic diagram shown in Fig-

ure 1 . The eight potentiometers are

connected to channels 0 through 7 of

the A/D converter IC1. The MAX186

IC, which has already been used in a

Elektor Electronics

2/2000

part of the AWE-64 package, for

instance, but it cannot be ordered sep-

arately. You can either buy one for

around £15 in a computer shop or copy

one of the numerous Elektor designs

(such as the MIDI interface in the 1995

Summer Circuits issue). A less elegant

option, but one that can conceivably be

used if no other MIDI devices are con-

nected, is to connect the MIDI para-

meter box directly to the 15-pin joystick

interface, which also has a MIDI input.

The 220

Table 1. Contents of the six layers within the three super-layers.

Layer

super-layer 1 (AWE, EMU8000 and EMU10k-1 synthesizers)

layer 1

Controller 10 – 17

layer 2

Controller 18 – 1F

layer 3

volume

pan

expression modulation

LP cutoff

LP reson.

chorus

reverb

layer 4 LFO1 delay LFO1 freq. LFO1 pitch LFO1 vol. LFO2 delay LFO2 freq. LFO2 pitch LFO2 vol.

layer 5 env1 delay env1 attack env1 hold env1 decay env1 sustain env1 release env1 pitch env1 cutoff

layer 6 env2 delay env2 attack env2 hold env2 decay env2 sustain env2 release

-, -

super-layer 2 (XG synthesizer)

layer 1

Controller 10 – 17

layer 2

Controller 18 – 1F

layer 3

volume

pan

expression modulation portamento

reverb

chorus

variation

layer 4

attack

decay

release

vib. delay

vib. rate

vib. depth

cutoff

resonance

layer 5

pitch init

pitch attack

pitch rel.

p.r. time

vel. lim. L

vel. lim. H

-, -

layer 6 pitch ben.

filter ben.

amplitude

ben.

LFO PMOD

ben.

FMOD D

ben.

AMOD

super-layer 3 (software synthesizer)

layer 1

Controller 00 – 07

layer 2

Controller 08 – 0F

layer 3

Controller 10 – 17

layer 4

Controller 18 – 1F

layer 5

Controller 20 – 27

layer 6

Controller 28 – 2F

provided by a simple 12 V mains

adapter. Diode D2 provides protection

against a reverse-polarity connection.

board that is the size of a pack of ciga-

rettes, as shown in Figure 2 . It is avail-

able from Readers Services (order

number 990087-1 ). You shouldn’t expe-

rience any problems mounting all the

components, which takes around half

an hour. Pay attention to the orienta-

tion of the electrolytic capacitors, the

LEDs and the ICs, and don’t forget the

wire bridge next to K5. After this you

can prepare the control panel. The

potentiometers and switches can be

glued to the front panel in a reasonable

arrangement, such as that shown in

Figure 3 , and wired using flatcable.

You can also mount these components

A S SMALL AS POSSIBLE

To make the construction of the MIDI

parameter box as convenient as possi-

ble, we have designed a printed circuit

Table 2. Meanings and uses of all switches.

Component

Designation

Meaning

LED D2

MIDI Message

Message Blinks when a MIDI message is sent via the MIDO OUT port.

Also blinks when a potentiometer is set exactly between two quantization levels.

LED D1

Init Value

Blinks after the power is switched on to indicate that one of the three

super-layers must be selected using switches S1 – S3.

Illuminated when the initial value is set for the potentiometer that was last rotated.

Switches S1 – S4

MIDI-Channel

These four binary-coded switches select the MIDI channel.

Potentiometers P1 – P8 Fader

These potentiometers are used to set the MIDI values.

Pushbuttons S1 – S6 Layer

These switches select layers 1 through 6.

Pushbutton S7

Memo

Save the last modified value in the current layer.

Pushbutton S8

Reset

Overwrite the current value with the predefined initialization value.

Elektor Electronics

2/2000

COMPONENTS LIST

C15

C16

Resistors:

R1,R8 = 1k Ω 5

R2 = 1k Ω

R3 = 10 Ω

R4,R7,R9-R16 = 10k Ω

R5,R6 = 220

C1 0

IC2

C14

Ω

P1-P8 = 47k Ω linear potentiometer

P9 = 470 Ω preset Hi

Capacitors:

C1-C8,C10,C11,C12,C14,C18 =

100nF

C9,C13,C17,C19 = 10µF 63V radial

C15,C16 = 33pF

C17

990087-1

C13

IC3

Semiconductors:

D1,D2 = LED, high efficiency

D3 = 1N4001

T1 = BC547B

IC1 = MAX186BEPP

IC2 = PIC16F84-10/P (programmed,

order code 996521-1 )

IC3 = 7805

Miscellaneous:

K1 = 4-way SIL connector

K2 = 2 PCB solder pins

K3,K6 = 10-way SIL connector

K4,K9 = 5-way SIL connector

K5,K10 = 6-way SIL connector

K7 = 15-way Sub-D plug, chassis

mount (see text)

K8 = 5-way DIN socket, chassis

mount, 180° (see text)

K11 = mains adaptor socket

S1-S8 = pushbutton, 1 make contact

S9-S12 = on/off switch

X1 = 10MHz quartz crystal

Enclosure, e.g. Teko 363

(216x130x77mm)

PCB, order code 990087-1

monitor should dis-

play control codes.

These will have values

ranging from 0 to 127.

If this does not hap-

pen, thoroughly check the circuit con-

struction, the cabling and the settings

of the MIDI monitor. If this doesn’t

help, you can curse Windows or the

sound card.

However, if the MIDI monitor dis-

plays the first MIDI events, then every-

thing is in order. Trimpot P9, by the

way, can also be used for calibration to

adjust actual range of the MIDI values

to 0 through 127.

Verify that the MIDI channel is

Figure 2. The MIDI para-

meter box can be build

using this small printed

circuit board.

changed by S9–S12

(binary), and that

changing the layer

works properly.

When the layer is

changed, the last stored values for the

potentiometers are always output via

the MIDI interface. The advantage of

this is that the parameters of the syn-

thesizer or the sound card are reset to

their last stored values. If for example

you change the volume in layer 3,

change to a different layer and some

time later return to layer 3, the volume

will be restored to its original level. If

you want to avoid this, all you have to

do is to press the Memo button before

on a piece of prototyping board and

wire them point-to-point. Of course,

you can also design a ‘real’ circuit

board. You should dress the flat cables

such that the unit can later be built into

an enclosure.

T ESTING

In order to thoroughly test the MIDI

parameter box, you absolutely need a

MIDI monitor with a MIDI-through

option for the PC, so that you can

observe the transmitted MIDI data on

the monitor and properly calibrate the

potentiometers. The text box contain

more information about suitable MIDI

monitors. After a visual inspection of

the soldering, connect the parts

together and cable the unit to the PC.

Then switch everything on and start

the MIDI monitor. All the stored values

in a virgin PIC are set to FFh, so they

must be set to valid MIDI protocol val-

ues by pressing the Reset button. Next

select super-layer 1 and layer 1 (the

default layer) by pressing S1 twice.

Now comes the moment of truth.

When the potentiometers are rotated,

LED D2 should flash and the MIDI

Elektor Electronics

2/2000

127

MRPC

MIDI REMOTE PARAMETER CONTROL

MIDI

DATA

INIT

VALUE

CHANNEL

LAYER

MEMORY

RESET

990087 - F

Figure 3. A reasonable

arrangement for the

control elements on

the front panel.

changing the layer. In this case only the

values that have changed since the last

layer change are stored.

Text editing

(German original): R. Gerstendorf

Design editing: K. Walraven

(990087-1)

MIDI monitors

There is a whole series of MIDI monitors that can be used with a

PC. An outstandingly suitable program is MIDI-OX, for which a beta

version is available for free on the Internet at

www.members.xoom.com/_XOOM/MIDIOX/moxbeta.htm. After

installing and starting the program, you must first select the MIDI

devices, either via the menu Options/MIDI Devices or by clicking

on the dark blue button with the five-pin DIN connector (see Figure

A ). On this PC, the MIDI input and output of the SoundBlaster SB16

are active.

The MIDI Port Activity window shown in Figure B appears if you

press the bright green DIN icon in the second group of buttons.

Each MIDI input and output gets its own row of ‘LEDs’, so that it is

clear which channel is active.

The content of the transmitted data appears in the Monitors Output

window. The first column shows the time when the MIDI message

occurred (as noted by MIDI-OX), and the second column indicates

the MIDI port via which the message arrived (in this case, Port 1 via

SB16 MIDI). The following byte, 0BFh, consists of two parts: a Con-

trol Change (indicated by the ‘B’) and the MIDI channel number

(indicated by the ‘F’, which corresponds to MIDI channel 16).

DATA1 shows the controller number (0 – 127 in this case) and

DATA2 shows the assigned value. Just as with DATA1, only the

lower seven bits are used, so that the values range from 0 to 127.

CHAN shows the MIDI channel once again. Note that MIDI officially

uses channel numbers 1 through 16, but many programs display 0

through 15. When a different super-layer is active or the layer is

changed, the messages displayed on the monitor also change.

If you want to learn more background information regarding MIDI,

you can find an adequate amount of literature on the Internet. One

example is Eddies Home – MIDI-RPN and NRPN

(http://members.delosnet.com.tlc/nrpn.htm).

MIDI-OX is especially well suited to checking equipment functions. If you want to go deeper into the matter, you can try easy-to-

use and powerful programs such as Generator from Native Instruments or Rebirth from Propellerhead. Free demo versions of both

programs are available. These can be used for only a very short time and have no save functions, but they are an outstanding

choice for just playing around with the MIDI parameter box.

Elektor Electronics

2/2000

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