What OSC_PARAM receives on KORG NTS-1

What this note is for?

--> Japanese version

Logue SDK custom oscillators can take up to 6 parameters which is controlled by B knob on KORG NTS-1. The custom oscillators can receive the value on OSC_PARAM function. It is documented on the official doc, but there looks some different behavior on the actual KORG NTS-1 devices.

In this note, I'll explain the actual values which your custom oscillator will receive on KORG NTS-1, including the un-documented part as well :) Please note that the undocumented part should be the subject to change.

NTS-1 device info

I used the following device to check the behavior below.

$ ./logue-cli probe
> Device: nutekt digital
> System version: 1.02
> Logue API version: 1.01-0
> Available modules:
...

Values for Developers and Users

The parameter value on B knob will be passed to OSC_PARAM. Developers will see this value on their custom oscillators.
OTOH, there is 7-segment display on KORG NTS-1 as well. Users will see the values here.
There are mismatches on both numbers in some cases. In this note, I'm using the following format to explain the both values for developers and users.

	min	zero	max
config	minimum value in manifest.json	-	maximum value in manifest.json
for devs	min value passed to OSC_PARAM	value passed to OSC_PARAM when we expect "0"	max value passed to OSC_PARAM
for users	min value on the 7-segment display	value on the display when we expect "0"	maximum value on the display

The italic value means that there will be some mismatches on the expected values or any offsets on them.

typeless values

It will be a typeless value if the 4th value of parameter definition is "" (empty) in manifest.json.

Explanation in the public doc

• In the case of typeless values, the minimum and maximum values should be positive.
• Also the displayed value will be offset by 1 such that a 0-9 range will be shown as 1-10 to the minilogue xd user.

Actual behavior on NTS-1

Case: minimum value = 0

This is not allowed based on the public doc, but it's possible to set. In this case, there will be a 1 offset. The OSC_PARAM will receive [0, 9], and users will see [1, 10] as documented.

	min	zero	max
config	0	-	9
for devs	0	0	9
for users	1	1	10

Case: minimum value > 0

This is a legit case based on the public doc. But surprisingly the offset, which is documented, is not applied in this case.

	min	zero	max
config	20	-	30
for devs	20	-	30
for users	20	-	30

Case: minimum value < 0

This is against the public doc though, it is possible to configure as well.
In this case, when the B knob points to the negative range, OSC_PARAM will receive the negative value. But please note that you will need to cast the 2nd arg to int16_t since it is uint16_t in the OSC_PARAM template.

void OSC_PARAM(uint16_t index, uint16_t value) {
  const int16_t value_i = (int16_t) value;

In addition, it looks that the 7-segment display can't handle negative values correctly at this point. It shows -999 for all negative values.

	min	zero	max
config	-100	-	100
for devs	-100	0	100
for users	-999	0	100

	min	zero	max
config	-30	-	20
for devs	-30	0	20
for users	-999	0	20

percentage values

It will be a perecntage value if the 4th value of parameter definition is "%" in manifest.json.

Explanation in the public doc

There are no specific explanations about percentage values in the public doc. So it is assumed that the following general restriction will be applied:

1. minimum value (int) : Value should be in -100,100 range.
2. maximum value (int) : Value should be in -100,100 range and greater than minimum value.

Actual behavior on NTS-1

Case: minimum value = 0

In case of percentage values, there are no offsets like typeless values, and the raw values will be shown for users as well. Easy to understand :)

	min	zero	max
config	0	-	9
for devs	0	0	9
for users	0	0	9

Case: minimum value > 0

No offsets as well. Simple enough.

	min	zero	max
config	20	-	30
for devs	20	-	30
for users	20	-	30

Case: minimum value < 0

It is a legit configuration, but there looks some undocumented behavior on it.
The OSC_PARAM will receive values with a 100 offset. As the result, its value range starts from 0 and your module will receive positive values only. You will need to subtract 100 from the raw value to have the expected number.

In addition, the 7-segment display shows weird numbers as well. If the B knob points to any negative range (it means OSC_PARAM is receiving [0, 99]), the display always shows 999.

	min	zero	max
config	-100	-	100
for devs	0	100	200
for users	999	0	100

	min	zero	max
config	-30	-	20
for devs	70	100	120
for users	999	0	20

On top of that, if the maximum value is a negative value, there'll be more weird behavior that the NTS-1 just ignore the maximum value and it will be considered to be set to 0. In the real use cases, I suppose it is not so usual to set negative values on both min and max values, so it won't be a big problem though.

	min	zero	max
config	-30	-	-20
for devs	70	-	100
for users	999	-	0

Appendix：k_user_osc_param_shape and k_user_osc_param_shiftshape

It is documented that they will be passed as a 10-bit value. More particularly, it means uint16_t value in a range of 0-1023. In the sample code in the official repository, it converts the int16_t into float by param_val_to_f32(). It applies a fixed factor internally to covert 0-1024 integer into 0.0-1.0 floating point value. If you don't need to have 0.0-1.0 value in your custom module, it is not always needed to apply param_val_to_f32() it looks.

Conclution

This note explains the actual values which your custom oscillator will receive on KORG NTS-1, including the un-documented part as well. Again, please note that the undocumented part should be the subject to change,.