CASIO MT-540   digital keyboard with atmospheric background sounds, clear percussion & MIDI

This digital keyboard with MIDI has each 20 preset sounds and rhythms. Its special feature is the "sound effect" section, which plays 8 atmospheric background sounds based on complex algorithmic patterns. These are no accompaniments but include environmental noises like "forest" or "ocean" and movie stuff like "wild western" and "space wars".

All sounds are made from medium resolution samples; many sound quite natural, others have organ- like timbres but none are really grainy; apparently some oversampling hardware prevents this. The timbre quality is higher and sounds a bit warmer than cheap Casio 100 ToneBank keyboards (e.g. Casio SA-1 or MA-130) although their squawky appeal is partly similar and like with these there are many unique and well recognizable sounds (but the 100 ToneBanks sound more extreme). The acoustic "piano" sounds very real and the natural drum kit percussion sounds way clearer and features astonishingly realistic cymbals. There are 2 keyboard effect kit modes for separately playing all the sounds from the "sound effect" patterns (one per key), those include also some wicked tekkno siren noises and space laser sounds.

All main voice sounds employ a stereo chorus effect and a small dose of reverb (those can not be turned off). Annoying is that many sounds include too long sustain. Don't be confused by the "210 sound tone bank" claim on the front panel; this instrument has only 20 preset sounds (including drum- and effect kit modes) those can be only layered to form 210 dual voice combinations. 10 additional sounds can be reached through MIDI or circuit bending. Unfortunately the accompaniment (during rhythm) accepts only standard establishment chords, although the "fingered 2" mode here at least layers any manual chord notes of "wrong" key combinations with the running accompaniment.

main features:

JASRAC, T-200240, MT-540

eastereggs:

modifications:

notes:

So far I remember, the Casio MT-540 has 10 hidden additional preset sounds those can be only accessed by MIDI, but these sounds can be also reached manually after an easy  modification. In comparison to the (newer) Casio CT-840, MA-130 and the SA-series keyboards, the sound quality of the earlier MT-540 is astonishingly high; especially the percussion sounds by magnitudes clearer than the latter. Possibly Casio squeezed the 100 ToneBank and 100 rhythm bank of these newer keyboards into the same amount of ROM space like the only up to 30 preset sounds and 20 rhythms of the MT-540 hardware. But the MT-540 CPU also employs an external ROM chip while with such later keyboards it became fully integrated into the CPU to reduce manufacturing cost. The PCB of the sample based MT-540 contains more components than these newer instruments, although already considerable less than the old semi- analogue Casio keyboards. The keys are easy going and well responding and you can nicely glide on them.

All main voice sounds employ a mild stereo chorus effect and a dose of reverb those can not be turned off. There are also neither sustain nor vibrato controls on this instrument and many preset sounds contain annoyingly long sustain. The sounds are genuine stereo (with different panning positions, not just a rotary speaker simulator) and apparently the sound generator employs oversampling because low notes turn duller (like with FM keyboards) and not rough and grainy like with most cheap sample based lo-fi tablehooters. Thus the preset timbres have high tone quality and sound fairly noble although not all of them are realistic. The sampled "piano" sounds astonishingly real and has about 7 split zones (much more than I found on other average home keyboards); you can even well here the woody knocking hammers with higher notes. (Only velocity is missing.) The "harpsichord" rather reminds to a funky clavinet or slap bass in the bass range and like many other timbres here it sounds a bit reedy and of plastic in the mid range, but it still sounds nice. The "funky clavi" is duller and especially has a dull bass range and reminds more to a fuzz distorted lead guitar (also with plastic mids). The "elec piano" has sustain and a slightly squawky timbre (semi- metallic, Rhodes imitation?, also a bit guitar- like with brassy mids); in the bass range a split zone makes it very dull (like a down sampled xylophone?). The "vibraphone" sounds nicely realistic (with 6Hz vibrato); the bass range is quite dull and woody. The "jazz guitar" is more a dull electronic organ timbre with mild tremolo (chorus effect?) decay envelope and dull bass range. The "jazz organ" is a slightly hollow Hammond imitation with percussive attack and mild chorus, while "organ" reminds to a clarinet or wooden pipe organ rank or the "synth reed" found on SA-series keyboards; it has chorus, a dull bass range and slightly longer reverb. The "pipe organ" is a bright metal pipe organ rank timbre, that reminds to the famous multipulse squarewave timbre, but is brighter, has chorus and a duller bass range, which makes it sound more like a transistor organ with a small dose of leslie and sustain; unusual is that volume decreases during the first 0.5s. The "accordion" sounds a bit of plastic in the mids, but otherwise quite natural (with semi- woody bass range). The "brass ens" sounds not at all what the name suggests, but is a thin sounding reedy plastic timbre with strange scratchy attack phase, chorus and a 4Hz vibrato that continues during its fairly long reverb. Possibly it is made from sawtooth waves; it has much similarity with certain thin C64 timbres; especially the (duller) bass range reminds to C64 organ bass sounds. (This sound has nothing to do with the famous SA-series "brass ens" but resembles rather "pop lead" on SA-series or the "magical wind" sound on Casio CZ-230S.) The "strings" fades louder and then quieter during the first second before it holds with fluttering tremolo. The timbre is a little bright and thin and even slightly resembles the bizarre "cello" on Casio CZ-230S although it lacks the drastic timbre change; the trebles have something of a mosquito, and there is a 2s long sustain (which often disturbs). The "flute" has a delayed 4Hz vibrato and while high notes resemble a metal flute, low notes are more like dull woodwinds. The "chorus" attempts to simulate a human choir, but the timbre is more like a dull synth brass chorus with slow attack and fluttering tremolo; the bass range is very dull. The "bells" is a grainy lo-fi timbre of long clanging church bells with a very long echo of repeating clangs (over 10s!); lower notes sound dull and disharmonic. The "synth ens" is a slightly sitar- like bright timbre with decay envelope, 6Hz tremolo and long sustain; the bass range sounds grainy and woody (reminding to some Miracle Piano timbres). The "bass" is a key split sound with a dull e-bass (or nylon guitar?) to the left hand and a funky hammering fat slap bass to the right hand. Great is that when a key is trilled, each new note occupies a new sound channel, which produces a great phasing sound and volume increase effect although this eats up polyphony. Like with many other MIDI keyboards, pressing semi- OBS preset sound buttons with held notes does not affect them in any way but only changes the sound of newly played notes (this can be also used for play tricks, especially with "sound effect" sounds).

"percussion" is a keyboard drum kit mode in stereo that sounds nicely realistic. Most sounds exist in a few different pitches and particularly remarkable are the 15 hifi cymbals and gongs made from loop samples with noticeable tremolo (but no truncated envelope); possibly the reason for the tremolo is that the loop sample plays alternatingly forward and backward to prevent clicks. Some cymbals bend their pitch up or down, which sounds quite unique. There are also 3 synth toms and latin percussion (agogo etc.). The 2 "sound effect" presets are effect kits (like keyboard drum kit modes) with all the samples from the "sound effect" section; many of them have very long sustain (14s), which can be annoying; sustaining sounds can be stopped by switching the accompaniment on or off (no matter if it is running) with the "chord/ midi" switch. Any 2 preset sounds can be layered by selecting one sound, pressing the "210 tone bank" button and selecting the second one.

There are 10 additional preset sounds those are only available through MIDI or circuit bending. The "metallic sound" is a sort of thin distorted lead guitar with halfway sitar- like timbre; it also reminds to a clavinet. "honkytonk piano" is like "piano" with slightly detuned chorus effect. "marimba" sounds like a plain xylophone with quite fast decay and dull bass range; the timbre is more like a short Hammond organ blip (resembling 2 operator FM). The "oboe" has a nicely sonorous woody bass range that resembles more an e-bass or saxophone and decays quieter during the first second. It could be also a semi- brassy pipe organ rank. The "synth reed" is a rock organ with vibrato (about 3Hz), mild chorus and a clarinet- like squarewave- timbre; bass range is duller than normal squarewave. (This sound also exists on Casio SA-series.) The "harp" has a dull bass range and much reverb; the timbre resembles the well known 2 operator FM synth harp sound. "synth celesta" has a bright timbre like a semi- metallic electronic organ chord (resembling Bontempi GT 509 sounds) and a weak echo during key release. "synth clavi" has detuned chorus and sounds like a hifi variant of the bright My Music Center "guitar" timbre, although the bass range is much duller and warmer. The "fantasy" sounds like a sitar and quickly howls up and down again during attack and has a 6s long, slowly pulsing sustain (sounds a bit shorter with longer key presses). The bass range is quite dull. The "miracle" has a slow attack phase and a glassy digitallic synth violin timbre that slowly alternatingly fades bright and duller (like a microphone feedback or bowed glass, a bit sitar- like). The timbre change continues during the 6s long sustain after key release. (A slightly similar "miracle" sound with howling pitch exists on Casio CZ-230S.)

The 8 preset "sound effect" buttons play atmospheric environmental noise patterns. Normally the sound effect pattern stops 9s after releasing the button, but when "hold" is pressed, it stays on until "hold" is switched off again. When "fade in/ fade out" is pressed together with a sound effect button, the pattern fades louder and stays on. When "fade in/ fade out" is pressed during the pattern, it fades quieter until silence. The pattern also stops immediately when when the sound effect volume slider is moved. The "forest" pattern contains the noise of a brook with bird and cuckoo voices. "ocean" is ocean waves noise with sea gulls (those whistle rather flute- like). "street" is car road traffic with honking car horns. "space wars" has an upward howling bass siren monoto in the background and various random space laser, explosion and tooting telephone touch tone noises (like historical videogame sounds). "rainy day" is varying rain noise. "evening" is locust chirping, frogs and woodpecker (?) noises. "concert hall" is varying strong applause with whistling and rhythmically clapping spectators. "wild western" sounds like galloping horses of varying speed with pistol shots. All these patterns are not just a boring loop sample (like the infamous sound effect of those mechanically animated Chinese waterfall picture lamps) but complex programmed algorithmic sound structures, those vary a lot over time in semi- random ways and thus sound much more realistic. Another keyboard with similar atmospheric sound patterns was the Casio SA-40.

sound art question: I remember that as a child I saw in TV an artist who created electronic sound sculptures of discrete analogue components (freely wired in a picture frame, one included a long ferrite antenna coil) those also synthesized natural environmental noises much like the "ocean" and "forest" pattern of the Casio MT-540. Nowadays there are various electronic relax devices (sometimes with alarm clock) to produce similar sounds, but I think this artist was likely the first inventor of them. Does anybody know his name?

The 20 preset rhythms are made from the percussion samples, have each an intro, fill-in and ending and also include unusual patterns with latin percussion those partly sound quite oriental; their style is similar like with Casio CZ-230S, although the timbres are clearer, brighter and sound a bit less woody. The semi- OBS preset rhythm buttons wait until the next bar before they switch a running rhythm. The tempo can be adjusted between fairly low and quite high (nothing really extreme).

The accompaniments have nicely unusual patterns, although they partly sound quite cheesy and over- orchestrated. E.g. the "march" has a cheesy flute arpeggio in it. Fortunately the arpeggio (or obligato) track can be muted by selecting the "fingered 2" mode. Many patterns have similarities with the Casio MA-130 styles. Unfortunately the accompaniment (with rhythm) accepts only standard establishment chords, but unusual is that the "fingered 2" mode at least layers any manual chord notes of "wrong" (non- chord) key combinations as additional notes with the running accompaniment. With rhythm off there is a manual chord mode with bass, which fortunately accepts also non- chords; while in "fingered 1" mode the bass sounds with every new note (and additionally as a trio when a standard chord is played), with "fingered 2" only the chord voice plays with individual notes, and the bass sounds only when a standard chord is played. The single finger chord mode sounds always like playing a standard chord. The employed bass and chord sounds in the accompaniments or manual chord modes depend on the currently selected rhythm.

There is also a simple record/ playback sequencer that records any played notes with accompaniment and sound change events, but it can not be edited.
 

circuit bending details

The hardware of the Casio MT-540 is based on the CPU "NEC D938GD" with 2 attached ICs those appear to be a ROM and a RAM. The control panel is connected through the 20 pin foil cables "JC" and "JB" and the keyboard through the 15 pin cable "JA". The keyboard output is routed through a separate IC, that is likely the MIDI controller and can interrupt the connection between CPU and keyboard to mute the internal sound generator when only used for MIDI output.

The Casio MT-240 looks almost exactly like the MT-540 and only lacks the sound effect pad section; I don't know if it has a different (or no external?) ROM or if here just some buttons were omitted (and likely some functions suppressed by a fixed matrix diode or buttons wired differently because the preset sound order is different) to sell it as a cheaper version. If the ROM is the same, it would be likely possible to upgrade the MT-240 (and other keyboards in its hardware class) with the sound effects of the MT-540.

keyboard matrix

JB8
JB9
JB10
JB11
JB12
JB13
JB14
JB15
 
pin
in 1
in 2
in 3
in 4
in 5
in 6
in 7
in 8
in/ out
 
P.
hold
P.
fade
o
o
o
o
o 
o
out 1
JC1
 P.
forest
P.
ocean
o
o
o
o
o 
o
out 2
JC2
P.
street
P.
space wars
o
o
o
o
o
o
out 3
JC3
P.
rainy day
P.
evening
o
o
o
o
o
o
out 4
JC4
P.
concert hall
P.
wild western
o
o
o
o
o
o
out 5
JC5
P.
volume 0
P.
volume 1
P.
volume 2
P.
volume 3
P.
volume 4
O.
30 sounds mode
key hold
 
out 6
JC6
C.
volume 0
C.
volume 1
C.
volume 2
C.
volume 3
C.
volume 4
 
 
 
out 7
JC8
R.
volume 0
R.
volume 1
R.
volume 2
R.
volume 3
R.
volume 4
 
 
 
out 8
JC9
C.
off
C.
fingered 1
C.
fingered 2
C.
single
C.
MIDI
power
standby
power 
disable (diode)
power
on
out 9
JC10
O.
percussion
O.
sound effect 1
O.
honkytonk
O.
marimba
O.
oboe
O.
synth reed
O.
harp
 
out 10
JC11
O.
piano
O.
harpsichord
O.
vibraphone
O.
jazz organ
O.
pipe organ
O.
brass ens
O.
flute
O.
bells
out 11
JC12
R.
16 beat 1
R.
disco 1
R.
pops 1
R.
slow rock 1
R.
swing
R.
samba
R.
bossa nova
R.
waltz
out 12
JC13
O.
select
R.
select
o
R.
fill-in
R.
start/ stop
R.
intro/ ending
R.
rock 1
R.
8 beat 1
out 13
JC14
O.
tone bank
O.
trio
o
o
o
o
o
o
out 14
JC15
demo
 
o
o
o
o
o
o
out 15
JC16
sequencer
record
sequencer
start/ stop
o
o
o
o
o
o
out 16
JC17
R.
tempo -
R.
tempo +
o
o
o
o
o
o
out 17
JC18

All unknown function names and in/ out numbers in this chart were chosen by me. The input lines are active- high, i.e. react on +Vs. Any functions can be triggered by a non- locking switch in series to a diode from one "out" to one "in" pin. Only "key hold" needs a locking switch.
 

legend:
"o"
 = keyboard key
underlined
 = function needs locking switch (i.e. stays active only so long the switch is closed)
R.
 = rhythm
C.
 = chord
O.
 = orchestra (main voice sound)
P.
 = sound effect pad
orange
background 		 = easteregg (unconnected feature)

  • main voice sounds ("tone")
    The Casio MT-540 normally has 20 main voice sounds, selected through 10 semi- OBS preset sound buttons and a select button for bank switch. As a matrix easteregg 10 additional preset sounds can be reached, but this is a little tricky. The additional 5 buttons for them have to be connected through diodes from JC11 to {JB10..JB14}. Instead of separate buttons I disconnected the JC12 line from the main PCB and inserted an alternating switch that either connects it with main PCB JC12 (like before) or with JC11. This way the additional matrix inputs can be reached through 5 of the normal preset sound buttons {vibraphone to flute}.

    But this is only half of the trick, because when used normally, you will only get 5 additional sounds because these new inputs ignore the "select" button (even the "select" LED unlights by pressing these buttons until you switch back to a normal preset sound). Possibly Casio planned here to release also a 25 preset sounds variant of this instrument, although I never saw any of these. To get the 30 sounds mode, a diode has to be connected at JC6->JB13 during power-on reset; when added or removed later, the CPU simply ignores it. But when enabled, the preset sounds are in different order and thus don't correspond to the control panel writing anymore. Instead of adding a fixed diode, for experimentation I wired it through the 2nd channel of that (2 channel) alternating switch, thus the 30 sounds mode is now only enabled when I switch it on during power-on, while otherwise everything stays normal. (The CPU ignores the diode when the switch is set later, thus the switch still enables the 5 sounds from the 25 sounds mode when switched later.)

    20 sounds mode: (5 additional sounds)
     
    PIANO
    HARPSI-
    CHORD
    VIBRA-
    PHONE
    JAZZ
    ORGAN
    PIPE
    ORGAN
    BRASS
    ENS
    FLUTE
    BELLS
    select 1, bank 1
    ELEC
    PIANO
    FUNKY
    CLAVI
    JAZZ
    GUITAR
    ORGAN
    ACCORDION
    STRINGS
    CHORUS
    SYNTH
    ENS
    select 2, bank 1
    PERCUSSION
    SOUND
    EFFECT 1
    PIANO
    HARPSI-
    CHORD
    VIBRA-
    PHONE
    JAZZ
    ORGAN
    PIPE
    ORGAN
    		  
    select 1, bank 2
    BASS
    SOUND
    EFFECT 2
    ELEC
    PIANO
    FUNKY
    CLAVI
    JAZZ
    GUITAR
    ORGAN
    ACCORDION
    		  
    select 2, bank 2
    -
    -
    HONKYTONK
    PIANO
    MARIMBA
    OBOE
    SYNTH
    REED
    HARP
    -
    select 3, bank 2

    The rows "select 1, bank 1" and "select 2, bank 1" correspond to the default preset button assignment of the unmodified Casio MT-540. The orange marked sounds are the 5 additional presets.

    The blue marked inputs apparently step an internal sound "select" register 1 step forward, i.e. when with active "bank 2" switch any blue marked button is pressed and the upper "select" LED was lit (i.e. select=1), then it advances to the lower LED (i.e. select=2), when the lower LED was lit, then both unlight (select=3), and when both are unlit (select is already =3) they stay this way. I don't know if this behaviour is a bug, or if it was intended for something technical.

    30 sounds mode: (10 additional sounds)
     
    PIANO
    HARPSI-
    CHORD
    VIBRA-
    PHONE
    JAZZ
    ORGAN
    PIPE
    ORGAN
    BRASS
    ENS
    FLUTE
    CHORUS
    select 1, bank 1
    JAZZ
    GUITAR
    BELLS
    FUNKY
    CLAVI
    METALLIC
    SOUND
    SYNTH
    ENS
    PERCUSSION
    SOUND
    EFFECT 1
    		  
    select 1, bank 2
    HONKYTONK
    PIANO
    ELEC
    PIANO
    MARIMBA
    ORGAN
    ACCORDION
    STRINGS
    OBOE
    SYNTH
    REED
    select 2, bank 1
    HARP
    SYNTH
    CELESTA
    SYNTH
    CLAVI
    FANTASY
    MIRACLE
    BASS
    SOUND
    EFFECT 2
    		  
    select 2, bank 2

    The orange marked sounds are the 10 additional presets.
     

  • separate rhythm & chord volume controls
    Despite the CPU supports separate digital volume controls for rhythm and chord using 5 step slide switches in the keyboard matrix, on this instrument only one common switch controls both simultaneously. Because the CPU remembers the last connected volume contact when all are disconnected (hearable by slowly moving the slider by one step back and forward) and both switches share the same input lines, instead of installing an additional 5 step switch it is much easier to disconnect JC8 (chord volume) and JC9 (rhythm volume) from the main PCB and reconnect them each through a separate button switch. This way both can be set independently because after the modification the switch connects either to the chord or rhythm volume input of the CPU only when the corresponding button is pressed (holding both buttons corresponds to the previous behaviour).
     
  • trio mode
    Adding a button here switches the main voice into trio mode (called "auto harmonize" by Casio), i.e. during accompaniment or manual chord the (now monophonic) main voice plays a trio corresponding to the current chord. Press it again to switch back to normal behaviour.
     
  • key hold
    This odd feature simulates that all main voice keys stay held down/ get stuck. Only after the instrument runs out of polyphony, the first pressed keys get freed again with every new key press. Switching it off immediately truncates any still sounding notes. Although this was likely intended for a hold pedal (existing on fullsize variants), also a switch here can be musically interesting to experiment with it. E.g. with decaying sounds this simply makes a longer sustain, and with continuous tones for tekkno trance etc. you get your hands free to play with the effect sounds etc. while the main voice stays constant.
     
  • digital power switch
    At JC10->JB14 there is a diode soldered in on the panel PCB. Removing it causes the matrix input JC10->JB13 to switch the instrument into standby mode and JC10->JB15 to power it on again. Likely a digital power switch was planned but not used here.
Unfortunately there is no easteregg to get rid of too long sustain or reverb.

attention: When a Casio keyboard (at least those without a list of preset sounds on the control panel) has a "210 Sound Tone Bank" or "465 Sound Tone Bank"  label, then it generally seems to have only 20 or 30 preset sounds (of those only any 2 can be layered to form that many a dual voice combinations) and thus has genuinely less preset sounds than the later Casio "100 ToneBank" instruments (of those e.g. my CT-840 still can layer any 2 sounds and thus can form even many more combinations). But at least non- professional 100 ToneBank keyboards seem to have a lower sample resolution. I am not sure if those 210 or 465 sound tone bank keyboards with sound list on the control panel (e.g. MT-740) are just different case variants of the same hardware family, or if they indeed can do more than layering 2 preset sounds.

Fullsize variants of the Casio MT-540 with 30 preset sounds (so-called "465 Sound Tone Bank") and trio mode were released as Casio CT-440/ CT-460 (49 keys) and CT-660 (61 keys). MT-540 variants without the "sound effect" pad feature were released as Casio MT-240 (case like MT-540 without pads) and MT-140 (in mono). Also the lower keyboard of the Casio DM-100 had this sound hardware (no MIDI, upper keyboard resembles Casio SK-8 main voice). Fullsize variants of the MT-240 were apparently the CT-370/ CT-380 (49 keys, no MIDI) and CT-607 (61 keys, no MIDI). These have no preset sound "sound effect" 1..2 and the rightmost 4 semi- OBS sound buttons are {flute, chorus, bells, percussion | synth-reed, metallic sound, synth ens, bass} (seen on Casio CT-370). The Casio MT-640 (bigger "dynamic bass" speakers, bulky case) had apparently a similar sound set but 4 sound effect pads and 6 orange rubber drum pads. A white Casio CT-460 version was released as Hohner PSK30 and a variant without "sound effect" (like with MT-240) as Hohner PSK50. (I don't know if Hohner also made midsize variants of these.) A keyboardless MIDI sound module with the MT-540 sound set (including all effects and even the demo, but like all these keyboards without velocity) was released as Casio CSM-1 and Hohner MSE-1.

question: Does anybody know whether any of these keyboards have a different ROM than Casio MT-540, or if there is just a diode or wire bridge somewhere to fool customers?
 

 removal of these screws voids warranty...    
WarrantyVoid
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