TSM 2040z Sub LowPass Filter

Although named as such, the TSM 2040z Sub LowPass Filter is not a typical Low Pass Filter. Such filters stem from the era of the earliest polyphonic synthesizers. They were designed in parallell to the filters of the monophonic synthesizers, and in the first stages of development produced bass enhancements at high resonance frequencies. However, they lacked gain compensation.
Returning to the beginings of filters, inspired us to create a Sub LP filter.
In TSM 2040z we retained the charm of the low frequency boosting characteristics of some early polysynth filters.
Bass Boost is adjustable up to the +12dB for the selected low frequency. The boosting of sub-frequency can be adjusted within the range 40-160Hz

Signals coming through the TSM2040z Lowpass filter are boosted with sub frequency enhancement.
The Lowpass section of the filter include various modes: Brickwall (which doesn’t have a slope) and Lowpass 12 / 18 / 24 / 30 / 36 / 48 dB/oct slope modes.
The Resonance curve changes the attenuation character of the resonance.
The Crasher can be used to add saturation or distortion as desired to the filtered sound as a filter-destruction effect.
The Limiter can be used to limit overclipping of the filtered signal keeping it warm, fat and soft.
Sub bass on the Resonance is the thing which makes it loveable.
Test the sub frequency boosting power of the TSM 2040z SLP filter for yourself.

Now TSM 2040z includes filter 3 modes:
- Sub LP Filter: Resonance Boost selected low frequency.
- Classic LP Filter: Resonance adjusts the resonant peak to the selected Frequency value. Boost of Low Freq is OFF.
- Hybrid LP Filter: Resonance adjusts the resonant peak to the selected Frequency value and Boost low frequency at the same time.

2040 - “Best filter chip ever”
SSM2040™ is one of the most famous filter chips produced during the era of early analogue polyphonic synthesizers.
The 2040 chip was used in many old and now rare analog synthesizers including the Prophet-5™ rev.2, RSF Kobol™. The 2040 filter sound is loved and highly rated by present day musicians.
Back in the day, synthesizer manufacturers were prone to swap out the SSM™ filter chips, which often had with defects, to more reliable CEM chips. Today, however, musicians look on the SSM™ 2040 as being the “best filter chip ever”.
The SSM2040™ is a very unique sounding filter which differs from all other 4-pole lowpass filters because it is based on the discrete OTA gain cell.
Over time, synthesizer manufactures turned predominantly to using CEM™ filters by Curtis™. These chips were more stable filters, but had a completely different character to the SSM™.
The SSM™, however, was to return as the brother 2044 filter chip used in Korg™ Polysix and other synthesizers). Today modern versions of the 2044 can be found in instruments such as Sequential™ (Dave Smith™) Prophet-5 and other modernclones.
In any case, musicians today hold the sound of the original 2040 filter with its own character in high regard.

A number of eurorack module designers created clones of the 2040. SynthesisTechnology™, for example, introduced the MOTM440™ module which modelled the sound of the 2040 but also incorporated a switch which added a low frequency boost at the higher resonance position.

TSM 2040z is not an exact emulation of the SSM2040™ chip filter or the MOTM440 module scheme. It aims instead to extend the capabilities of the well known vintage sound in its own particular way.
TSM 2040z is a type of the Sub LowPass filter. We tried to compensate for the bass which is lost with increasing resonance by adding an Adjustable boost with a range up to 12 dB.

Selectable low boost frequencies allow for the character of the sound to be altered to taste.
Boost adjust adds low frequency loss compensation.
Resonance curve changes the attenuation character of the resonance.
The Crasher can be used to add saturation or distortion as desired to the filtered sound as a filter destruction effect.
The Limiter can be used to limit overclipping of the filtered signal keeping it warm, fat and soft.

MODE SECTION

This is a Filter based on the idealogy of the early polysynthesizers [low frequency boost at Resonance rise] with various LP modes:
- BrickWall
- LowPass 12/18/24/30/36/48 db/oct slope

FILTER MODES:

• Sub LP Filter: Resonance Boost selected low frequency.
• Classic LP Filter: Resonance adjusts the resonant peak to the selected Frequency value. Boost of Low Freq is OFF.
• Hybrid LP Filter: Resonance adjusts the resonant peak to the selected Frequency value and Boost low frequency at the same time.

BOOST

The early filters found on the first polysynths produced bass enhancements at high resonance frequencies. However they lacked gain compensation.
Booster - is a psycho-acoustic low shelf filter.
In the TSM 2040z we retained the charm of the low frequency boosting characteristic to some early polysynth filters.
Bass Boost is adjustable up to the +12dB for the selected low frequency.

Resonance - sets the depth value of the Low Boost when in the On position.
When Boost is disabled (Off), Resonance parameter works in normal mode and does not boost the signal.
Resonance Smooth - smoothing of the Resonance changes
Boost Adjust - boost level of the selected Low Frequency in range +1..+12 dB
Boost Frequency - frequenecy of the Low Boost. Sub-bass frequency range: 40-160Hz

CRASHER

The Crasher effect controls the sample rate and bit depth of the audio signal and is used for adding saturation or distortion to the filtered sound.

Crasher On/Off - enable or Disable Crasher effect
Depth - Dry/Wet mix of the Crasher effect
Bits - Bit reduction
Sample Rate - downsampling rate
Freq Modulation Source: Depth, Sample Rate, Jitter
Reso Modulation Source: Depth, Sample Rate, Jitter

FM - set the level of the frequency modulation. FM Input placed at the rear panel

Update 1.1.0

• Bugfix: Filter no longer clicks with short pauses in the audio.
• Bugfix: Device sometimes not sleeping to save CPU when silent.

• Bugfix of the Resonance work in various filter type-modes

• Now 3 FILTER MODES. Press to BOOST pop-up button and select between 3 filter modes:
  1) Sub LP Filter: Resonance Boost selected low frequency.
  2) Classic LP Filter: Resonance adjusts the resonant peak to the selected Frequency value. Boost of Low Freq is OFF.
  3) Hybrid LP Filter: Resonance adjusts the resonant peak to the selected Frequency value and Boost low frequency at the same time.

Update 1.0.1:
- Fixing bug of FM modulation knob (in few filter modes (LP18, 30, 36, 48) no reaction to FM changes)
- Fixing bug of Crasher modulations