Figure 488. PC2A T-Type Leveling Amplifier.A. Clipping LED B. PC2A T-Type Leveling Amplifier enable/disable C. VU meter D. Limit/Compress E. VU meter mode F. Gain G. R37 H. Peak ReductionPC2A T-Type Leveling Amplifier is meticulously modeled after a legendary vintage electro-optical tube compressor. This compressor, known for its automatic gain control characteristics, delivers vintage sound with incredibly warm and rich compression. It is revered by audio engineers worldwide for its trademark sound, and has been used on countless hit records since the late 1960s. It is one of the true classics in the audio recording industry.The purpose of PC2A T-Type Leveling Amplifier is to limit the dynamic range of a signal by reducing the amplitude of its transient peaks. PC2A T-Type Leveling Amplifier varies its gain in response to the level of the input signal. Large input signals result in less gain, thus reducing or “compressing” the dynamic range of the signal.
Clipping LED. Shows if the input signal to the PC2A T-Type Leveling Amplifier module is clipping. If there is any distortion in the ProChannel signal chain, the clipping LEDs let you identify where the clipping occurs.
PC2A T-Type Leveling Amplifier enable/disable . Enables/disables the PC2A T-Type Leveling Amplifier module.
Limit/Compress. Changes the dynamic processing ratio between compressor and limiter. The compression ratio fluctuates depending on the frequency of the incoming signal.
Compress. In Compress mode, the compression ratio ranges between 3.5:1 for low frequencies and 6:1 for high frequencies. This method is suitable for leveling and reducing the general dynamic range of individual instrument tracks such as vocals and drums. It produces a more gentle compression.
VU meter. The VU meter can be switched to show gain reduction or output level, depending on the position of the VU meter mode knob.
VU meter mode. Switches the VU meter to show gain reduction or output level.There are four available modes:
GR. Displays the instantaneous gain reduction in dB. During periods of no gain reduction, the pointer will return to 0 VU on the meter scale.
+10. Displays the post-processing output level, referenced to +10 dBm (analog emulation).
+4. Displays the post-processing output level, referenced to +4 dBm (analog emulation).
dBFS. Displays the post-processing output level in the digital domain. This is the true output meter for digital audio, and is the recommended setting when monitoring output level.
Gain. Adjusts the post-compression output level, or make-up gain. Use this control to make up for the gain lost by the peak reduction. The Gain knob has no affect on the amount of compression. To adjust the knob in fine increments, hold down the SHIFT key while moving the knob.
Peak reduction. Adjusts both the threshold and the amount of compression (gain reduction). If the input signal level is below the threshold, no compression takes place. Turn the knob clockwise for more compression, or counter-clockwise for less. To adjust the knob in fine increments, hold down the SHIFT key while moving the knob.
R37 (High Frequency Pre-emphasis trim). Adjusts the gain reduction frequency response. The original hardware unit was designed for leveling in radio and TV broadcast applications. Due to an increase in high frequency content in FM broadcasting, the R37 control adds gain reduction at frequencies above 1kHz, based on the program material. Use this control to reduce or prevent over-modulation caused by the pre-emphasis (high-frequency sensitivity). When set to the FLAT position, gain reduction is applied equally on all frequencies. When the control is moved toward the HF position, gain reduction is increased on the high frequencies. Experiment to achieve a good balance between low and high frequency limiting. This control is often useful for de-essing vocals (cut down sibilance by compressing high frequencies), but the FLAT setting is recommended for most music applications. To adjust the knob in fine increments, hold down the SHIFT key while moving the knob.The purpose of a compressor is to limit the dynamic range of music or sound. Compression will make the loud parts of the signal more quiet, resulting in a more or less even level. Compression is usually applied to compensate for the small variations in level that occur when a musician plays an instrument or a vocalist sings a song.PC2A T-Type Leveling Amplifier is a soft-knee compressor that features program dependent release times and a flat frequency response of 30Hz to 15kHz (see for frequency response adjustment) The attack time is fixed at 10 milliseconds. The release time is roughly 60 milliseconds for 50% release, and 0.5 to 5 seconds for full release, depending on the previous program material. The two-stage release results in very transparent compression characteristics.PC2A T-Type Leveling Amplifier models the tubes and the T4 electro-optical device in the original hardware units. The T4 circuit uses an electroluminescent panel to determine the attack time, and an optical photo cell to determine the release time. All based on the incoming program material. The T4 has very little distortion. To realize the characteristic sound of the original hardware, the tubes are also modeled to add analog characteristics. Total Harmonic Distortion (THD) comes from the four tubes in the original hardware, which slightly changes the signal shape adding even and odd harmonics based on the frequency of the program material. The THD has a slight effect on the output gain, less than 0.35% to 0.75% at +10 dB to +16 dB of the program material.The modeling of the tubes and the T4 circuit is what gives PC2A T-Type Leveling Amplifier its unique compression characteristics. The curves are “wobbly” and only reduce gain to a certain point before “giving in” and letting the output level increase again. Unlike typical dynamics processors that have a fixed compression ratio across all frequencies, the PC2A T-Type Leveling Amplifier gain reduction is different at different frequencies.PC2A T-Type Leveling Amplifier is suitable for just about any audio material. It sounds especially good on vocals, and also works great on guitar, electric and upright bass, guitars, piano, wind instruments, and other tracks that need gentle compression. It even works well on full-program mixes.
PC2A T-Type Leveling Amplifier is suitable for just about any audio material. It sounds especially good on vocals, and also works great on guitar, electric and upright bass, guitars, piano, wind instruments, and other tracks that need gentle compression. It even works well on full-program mixes.Percussive instruments that have a lot of peaks, such as drums, may require more care. Although PC2A T-Type Leveling Amplifier works great for certain kick drum sounds, you may want to combine PC2A T-Type Leveling Amplifier with another compressor with a faster release time and more precise control. For details, see Using PC2A T-Type Leveling Amplifier on drums.Unlike a traditional compressor that has Ratio, Threshold, Attack, Release and Make-up Gain controls, PC2A T-Type Leveling Amplifier is very straightforward with only two primary controls: Gain and Peak Reduction. Peak Reduction controls the amount of compression and Gain controls the post-processed output level.The most common problem caused by the use of a compressor/limiter is excessive distortion. This normally indicates that the limiter is active too much of the time (threshold is too low). To correct the distortion, turn the Peak Reduction knob counter-clockwise.
2. Right-click any ProChannel module header and make sure Post FX Bin is not selected on the pop-up menu. In most situations, you want to apply compression before effects like reverb and delay.
3. While listening to the project, adjust the Peak Reduction control until the compressor exhibits the desired amount of compression. You may want to set the VU meter to show gain reduction (GR). A good target is to keep the gain reduction around 4-8 dB continuously.
4. If desired, adjust the R37 (pre-emphasis) control according to the amount of high frequency content in the audio material. Turn the knob counter-clockwise to increase compression of high-frequency content, such as vocal sibilance.
5. Adjust the Gain control to achieve the desired output level. You may want to set the VU meter to show output level (dBFS, +10 or +4).
6. By itself, however, PC2A T-Type Leveling Amplifier is not well-suited for compressing drums and other percussive instruments that have lots of peaks. The reason is due to the slower release time and lack of precise control, thus changes in the input level cannot be compensated for quickly enough to make the output volume totally consistent.A good compression trick is to chain different compressors together on the same track. This lets you use another compressor with a faster release time and more precise control as a peak limiter to first tame the peaks before they reach PC2A T-Type Leveling Amplifier, then use PC2A T-Type Leveling Amplifier for general compression.
As a starting point, place PC76 U-Type Channel Compressor in front of PC2A T-Type Leveling Amplifier. Configure PC76 U-Type Channel Compressor as a peak limiter: set a high compression ratio, like 12:1, and a fairly fast attack and release. Set the Input Gain carefully so the highest peaks are reduced by 2-3 dB, then adjust the Output Gain until you can’t hear a difference between the pre- and post-processed level (frequently enable/disable PC76 U-Type Channel Compressor so you can compare the pre- and post-processed levels). The goal is to only flatten the highest peaks, and not compress the overall audio signal.Next, configure PC2A T-Type Leveling Amplifier for general compression: set Compress/Limit to Compress, and adjust Gain and Peak Reduction to taste.In summary, first use a compressor with precise control to act on the peaks, followed by PC2A T-Type Leveling Amplifier for general compression.
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