ToolMod Pro Audio
Stereo Mastering Peak Limiter TM215b

Extremely fast Peak Limiter with additional Features for Stereo Mastering

The TM215b is a Stereo Mastering Peak Limiter with precise stereo tracking that can catch short peaks without audible side effects. The module operates without colorization and will not alter the sound under regulation. It is fast enough to react within the first period of a 20 kHz sine wave signal. Additional features allow better handling of the physical limitations with fast attack and release times. The TM215b is usually used directly at the end of an analog mastering chain. The output level can be adjusted without affecting the limiter setting.
  • extremely fast Stereo Peak Limiter for Mastering
  • LF-Attack for better Handling of low Frequency Attack Distortion with fast Attack-Time Settings
  • Dynamics Release for program-dependent Release Behavior
  • Static Attack
    from 20Ás to 7 ms
  • Static Release
    from 50 ms to 3 sec
  • Threshold adjustable
    from -10 to + 20 dB
  • Threshold ▒ 2 dB
    Fine Control
  • Output Gain ▒ 10 dB
  • Headroom + 30 dBu
  • Dynamic Range
    125 dBA/122 dBRMS
Stereo Mastering Peak Limiter Stereo Mastering Peak Limiter TM215b
The Basics
The Stereo Mastering Peak Limiter TM215b has been optimized for the use as output limiter of an analog stereo mastering processing chain. The attack time of this feedforward VCA limiter that uses a special peak detector circuitry is extremely fast and reacts within the first period of a 20 kHz sine wave. This quality is the most important qualification of a limiter that drives the A/D converter at the end of a mastering chain. In combination with a compressor that is optimized for high loudness gain, which requires a long attack time, the limiter takes care of an effective control of the signal peaks that will pass the compressor without causing any regulation. This setup is necessary to increase the A/D converter input level as close as possible to 0 dBFs without overload.

The TM215b stereo limiter does not alter the sound below and above threshold. Peak regulation of 3 to 6 dB will not cause audible side effects with an appropriate setting of the parameters under consideration of the physical limitations of any analog limiter but increase the loudness by suppression of the peaks.

Possible Gain Reduction and physical Limitations
The maximum gain reduction of the stereo limiter is way more than 20 dB; however, the feasible gain reduction is a lot lower and limited by the physical limitations of analog limiters. These are low frequency distortion with short release times and attack distortion in the bass range with fast attack times.
Low Frequency Distortion with short Release Times
When optimizing the release time in a way that pumping barely disapears, low frequency distortion due to regulation within the cycle duration of the audio signal is one of the issues that determines the maximum gain reduction. Depending on the portion of low frequency components at high levels in the output signal, a gain reduction of 3 to 6 dB is realistic und possible without negative side effects.
Dynamic Release
The dynamic release control, which is actually a variable version of the well known Auto-Release feature of some compressors, which is adapted to the special operation parameters of a limiter, is useful for preventing lf-distortion. Dynamic release increases the release time with high density signals which are in most cases equivalent to high levels in the bass range. By careful adjustment it is possible to find a better compromize between audible pumping and lf distortion than by using the static release control alone.
Static Release
In order to allow precise optimization of the Release Time, the control range is extended down to a value far below the optimum value of approximately 0.3 sec for pump free operation. Although a release time setting of less than 0.3 sec is not possible with low frequency signals, the range below can be used with audio signals with no considerable low frequency components. Such short release times increase the density of the audio signal. The minimum release time is 50 ms; the longest release time is 3 sec. A long release time will cause pumping but offers the choice to adjust a wide range of conventional settings, as they are used with broadcasting.
Attack Distortion
Attack distortion is the second important physical limitation. Due to the necessary very fast attack that is necessary to prevent overloading the a/d converter inputs, the limiter warps the wave form of a low frequency signal as soon as the level exceeds the threshold. The effect disappears with an attack time of about 1 ms; however, 1 ms is way too long to prevent short peaks from overloading the a/d converter. Even though the distortion only shows up during the first peak, it can be audible if the spectrum of the lf signal does not contain a wide range of harmonics. Unfortunately, there is no perfect way to avoid this effect but to reduce the gain reduction. The TM215b comes with a special LF-Attack circuit that allows better handling of this problem.
LF Attack
The TM215b comes with a LF attack control that works like some kind of low frequency soft knee function. Unlike the well known soft knee, lf attack affects the wave form of the bass signal when the limiter kicks in. The pot determines the frequency where the smoothing takes place. This means that a higher setting is not necessarily the better choice. If attack distortion appears, just find the best setting for the particular problem
Static Attack Time
Only the shortest possible attack time of 20 µs is important when using the TM215b as peak limiter with signals that contain very short peaks in the upper mid and high frequency range. With this setting, the limiter reacts within 8 Ás from the time when the momentary value exceeds the threshold and the regulation takes place. Since negative time is not possible, this delay will cause the first half wave of a 20 kHz sine wave signal to pass thru without full gain reduction while the second half wave is regulated down to the threshold level. Longer attack times will cause short peaks to pass thru the limiter. However, a longer attack time reduces the attack distortion problem. Therefore the best attack time setting depends on the occurence of short peaks in the upper mid and high frequency range. Choosing the longest attack time that still catches high frequency peaks ist always the best choice. The attack time control range reaches up to 7 ms to offer the choice of using the TM215b for other applications than stereo mastering as well. A longer attack time is well suited to use the device as additional, hard compressor that can add some density above a threshold level.
The Threshold can be adjusted in the range from -10 dB to + 20 dB. The 0 dB position is internally calibrated. The additional Vernier pot serves as fine control for the threshold with a range of +/- 2 dB.
The Output Gain Control with +/- 10 dB range and precisely calibrated 0 dB position at the center detent affects only the output level but not the settings of the limiter. After adjusting the limiter, the gain control is used to adapt the output level to the A/D converter connected downstream of the limiter.
Gain Reduction Display
Gain Reduction Display is a LED bar graph with 5 LEDs and 10 dB display range.
The TM215 Stereo Mastering Peak Limiter is a 2U ToolMod module that can be used in all ToolMod frames. As usual, horizontal and vertical versions are available.
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Price: € 625.00
excl. of VAT and Shipping
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Test Reports
-h: horizontal
-v: vertical
technical Specifications
Control Elements
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Picture v-Version
ToolMod Manual
TM215b Manual


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The TM222 Stereo Mastering Compressor is the best possible supplement to the TM215 Stereo Limiter. The combination of both devices forms a very effective dynamics processing tool for mastering.