Korg M3: Programming a Laser Harp
korg_m3.jpg

For this second tutorial, we are going to program a laser sound such as those used by Jean Michel Jarre.

As a reference, we may use a patch programmed by Barb from “Audiokeys.net” written for the Kurzweil PC3. You can listen to it here.

This patch uses a swatooth for oscillator n°1 and a square wave for oscillator n°2. According to its authors, most of the sound character is due to the oscillator’s synchronization. The Korg M3 do not have such feature, so we will have to find a workaround.

Here we go…

Oscillators

1. Hit the “Prog” buton to put your Korg M3 into “Program” mode.
2. Select bank F or G
3. Using the dial, find an “empty” program (intitled “InitProg”)

osc_init_prog.gif

4. Hit the “Page Select” button and then select “P1 Basic/DT/Ctrls”.

osc_P1_selection.gif

5. Ensures that the “Program Basic” tab is selected and check “Double Oscillator” Mode.

osc_double_osc_selection.gif

6. Hit the “Page Select” button and then select P2 OSC/Pitch
7. Ensures that the “OSC1 Basic” tab is selected
8. Use the sample “0658 : Saw”
9. Assign “-00.2 [Hz]” to the ‘Freq Ofs’.

osc1_settings.gif

10. Select the “OS2 Basic” tab and use the “0690 Square-EXB” sample for the second oscillator
11. Assign “-1[16’] to the “Oct” parameter in order to lower the second oscillator pitch by one octave.
12. Apply a “+00.2 [Hz]” to the ‘Freq Ofs’.

osc2_settings.gif

Now, you should have a first oscillator with a saw wave and a second one with a square wave at one octave below. Both oscillators are slightly detuned.

You can hear the result here :

Important: you can save you work at any time by clicking on the “down arrow” located in the upper right part of the screen and selecting the “Write Program” option.

Filter arithmetic

Let’s compare our sound time-frequency spectrum versus the original sound. Remember that the x-axis represents the time, the y-axis represents the frequency and that the colors represent the level.

filter_original_spectrum.png

There are several things to notice here.
First, you may see that the filter is closed at the beginning of the sound and then open suddenly to it maximum value.
Second, the red line represents the evolution of the filter cut-off frequency over time: the filter frequency is reduced over time. This kind of behaviour can be easily reproduced using the Filter Envelope Generator
Third, the dotted lines: this sound is very complex and the harmonics generated by the saw & synchronized square oscillators have a very specific shape. I’ve highlighted in orange two main harmonics with dotted lines. You can see that its frequency varies over time…Moreover there are plenty of these harmonics. These are clearly the most difficult points to handle with the M3.

Here is the spectrogram of our sound obtained by playing a C3….

filter_2oscillators.png

So you can see on the spectrogram that the sound spectrum cover all the frequencies. So we will have to set a low pass filter and make the cut-off frequency decrease from 10000Hz down to 3000Hz in about 4 seconds.

1. Hit the “Page Select” button and select “P3-1 Filter1”
2. Select the “EG” tab and enter the following settings

Level Start : -99 Attack : 0 Break : -30 Sustain : -30 Release : -30
Time Attack: 10 Decay : 87 Slope : 70 Release : 70
Curve Attack :0L Decay : 9 Slope : 0L Release :6
filter_EG1.gif

3. Select the “Mod” tab and apply a +99 Filter EG intensity to A.

filter_modA1.gif

4.Select the “Filter1” tab , chose a single filter. Select Low pass filter with a 70 cut-off frequency, and a 56 resonance.

filter_filterA1.gif

5. Hit “Page Select” button and select “P3-2 Filter2”
6. Select the “EG” tab and enter the following settings

Level Start : -99 Attack : 0 Break : -30 Sustain : -30 Release : -30
Time Attack: 10 Decay : 87 Slope : 70 Release : 70
Curve Attack :0L Decay : 9 Slope : 0L Release :6
filter_EG1.gif

7. Select the “Mod” tab and apply a +99 Filter EG intensity to A.

filter_modA2.gif

8. Select the “Filter2” tab, chose a single filter. Select low pass filter and apply a 72 filter cut-off frequency and a 00 resonance.

filter_filterA2.gif

Now you can hear the result here and see also compare the obtained time-frequency spectrogram of our sound and the original sound.

You can see that the filter cut-off frequency is not really the same as in the original sound. This is simply because it sounds better like this. Remember that we are not using the same hardware neither the same samples.

filter_lowpassfilter.png

So we still miss these harmonics that were plotted with dotted on the sound spectrogram. To add these to our sound, we are going to use the second filter of each oscillator.

1. Hit “Page Select” button and select “P3-2 Filter1”.
2. Select the “Filter1” tab.
3. Chose a “Parallel routing” and a “band pass” filter for filter B with a 57 cut-off frequency and a 52 resonance.

filter_parallel1.gif

4. Select the “Mod.” Tab.
5. Apply a +25 “intensity to B”

filter_parallel_mod1.gif

You can hear the output of the Band Pass filter here.

The following figure illustrate the spectrogram of the Band Pass filter output.

filter_bandpass1.png

Nb : to enhance the effect, this is the spectrogram on the figure was obtained with an higher resonance setting.

6. Hit “Page Select” button and select “P3-2 Filter2”.
7. Select the “Filter2” tab
8. Chose a “Parallel routing” and a “band pass” filter for filter B with a 34 cut-off frequency and a 74 resonance.

filter_parallel2.gif

9. Select the “Mod.” Tab.
10. Apply a +50 “intensity to B”.

filter_parallel_mod2.gif

.

You can hear the output of the Band Pass filter here.

The following figure illustrates the spectrogram of the Band Pass filter output.

filter_bandpass2.png

Nb : to enhance the effect, this is the spectrogram on the figure was obtained with an higher resonance setting.

If you listen to our reference, you may remark that the higher note sounds brighter than the lowest one. This can be done by modulating the filters cut-off frequency and resonance with the keyboard track feature.

11. Hit “Page Select” button and select “P3-2 Filter1”.
12. Select “Key Trk” tab.
13. Enter the following values :

Intensity to A : 99 Intensity to B : 99
Key KeyLow: F2 Center: C4 KeyHigh: C6
Ramp BtmLow:-50 LoCent: -50 CentHi: 0 HiTop : 0

This allows modulating the filter frequency according to the key pressed. Lower note will lead to lower filter frequency.

filter_keytrack.gif

14. Select the “Filter1” tab
15. For the filter A : In the Resonance AMS (look at the screenshot to locate it on the screen), select the “Filter KTrk” parameter. This allows modulating the resonance according to a given parameter, in our case the Keyboard Track parameter.

filter_parallel_mod1.gif

16. For the filter A : In the Resonance AMS Int. (AMS intensity), select +35. This specifies the amount of modulation.
17. For the filter B : In the Resonance AMS, select the “Filter KTrk” parameter.
18. For the filter B : In the Resonance AMS Int. (AMS intensity), select +40. This specifies the amount of modulation.

filter_AMS.gif

Nb : no modulation is used for filter 2.

Amplifier

We are going to add a little bit of overdrive to introduce high frequency harmonics that will help us to make the sound “richer”.

1. Hit the “Page Select” button and select “P4 Amp/EQ”.
2. Select the “Amp1/Driver1” tab.
3. Apply a 61 drive and 50 boost level.
4. Reduce the Amp level down to 50.

amp_driver1.gif

5. Select the “Amp2/Drive2” tab.
6. Apply a 43 drive and 34 boost level.
7. Reduce the Amp level down to 50.

amp_driver2.gif

You can hear the sound here.

Now it’s time to define a nice envelope for our sound.
8. Select the “Amp1 EG” tab.
9. Apply the following envelope settings:

Level Start : 99 Attack : 99 Break : 56 Sustain : 56
Time Attack: 0 Decay : 40 Slope : 40 Release : 67
Curve Attack :0L Decay : 40 Slope : 40 Rel :67
amp_EG1.gif

10. Select the “Amp2 EG” tab.
11. Apply the same envelope settings:

Level Start : 99 Attack : 99 Break : 56 Sustain : 56
Time Attack: 0 Decay : 40 Slope : 40 Release : 67
Curve Attack :0L Decay : 40 Slope : 40 Rel :67
amp_EG2.gif

Finaly, let’s modify the equalization a little bit to enhance the low frequencies:

12. Select the “EQ” tab.
13. Apply the following settings

LowGain : +11.5 dB MidFreq : 3.21 Hz MidGain : 0dB HighGrain : 0dB
amp_eq.gif

You can hear the sound here.

We can compare the time-frequency spectrogram of our sound with the original one. It’s far from being perfect, but there are some similarities.

Our sound
amp_enveloppe_eq.png
Original sound
amp_original_sound.png

Effect

In program mode, you can add effects to your sound. Many effects are available: reverb, chorus, delay, compression, flanger, phaser, etc.

In our case we are only using a the Chorus effect:
1. Hit the “Page Select” button and select “P8 IFX”.
2. Select the “Routing” Tab and sets the “Bus (IFX/Output )Select” parameter to IFX1.
This sends the oscillators output to effect n°1

effect_routing.gif

3. Select the “IFX Setup” tab
4. For effect n°1, chose “026:Stereo Chorus”

effect_IFX.gif

5. Select the “IFX1” tab
6. On the upper right corner of the screen, there is a “P” with a menu at its right. This allows selecting effect presets. We are going to use the “P01:Super Chorus” preset.

effect_chorus_off.gif

7. At last, do not forget to switch the effect on by clicking on the green button located in the upper left part of the screen, at the right of the effect name.

You can hear the result here:

Ok now, you can compare the time-frequency spectrogram of our sound and the original one. You can visualize the chorus effect on the sound spectrum.

Our sound
effect_chorus.png
Original sound
amp_original_sound.png

Conclusion

That’s all for today. The result is not too close from the original, but we still have something that sounds like a laser harp.
Here is a cover of Rendez Vous III (JM Jarre):

Probably using specific samples would help reaching a better sound. You may also investigate the "unison feature" available in monophonic mode (see “P1 Basic/DT/Ctrls”).
At each note played on the keyboard, this allows playing simultaneously up to 6 slightly detuned version of our program, leading to a very "fat" sound…

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