Technology Institute for music educators ti: me course 2a Advanced Sequencing, Second Edition

Example: High Pass Filter

1. 
   In pop/rock mixes high pass filters (HPFs) are used to clean up the low end of the mix. For example, to clear the way for the kick drum or bass, HPFs are placed on guitar, keyboard and some drum tracks. In such a situation, you would begin by setting the filter cutoff frequency at 100 – 400 Hz depending on the track, then adjust until you find the right cutoff frequency.
   
2. 
   HPFs might also be used to remove noise from a signal. If noise from a ground problem is present it can be reduced by passing the signal through a HPF with a cutoff freq set above the frequency of the noise. In this example, the cutoff frequency would be set just above 60 Hz.
   
3. 
   Low pass filters (LPFs) are used less frequently. Some microphones manufactured today have a significant boost in the higher frequency range. If the resulting signal sounds too “brittle,” a low pass filter can be used. To avoid a drastic reduction of frequencies above the cutoff frequency, try using a shallow slope (e.g., 3 dB/octave).
   
4. 
   Low pass filters are sometimes used to help create the effect of someone talking though an “old fashioned” telephone. In this case, the cutoff frequency would be set quite low (500 – 700 Hz) with a very steep slope.
   

Ratio: Sets the amount that the input signal needs to increase to cause a one-decibel increase at the compressor’s output. For example, with a 5:1 ratio, for every 5dB that the signal exceeds the threshold, the output will increase 1 dB. So, if the threshold is set at -10dB and the signal actually “hits” 0dB, the compressed signal level is -8dB.

Attack time: sets the amount of time it takes a compressor to start working after a signal exceeds the threshold. Fast attack times can alter the perceived frequency response of a signal. Since much of the high frequency content is contained in the attack of a sound envelope, compressing the attack can result in a dull sound. Try starting with longer settings and gradually moving to a shorter attack time.

Release time: determines the amount of time it takes the compressor to return a signal to unity gain (i.e., to stop attenuating) after the signal drops below the threshold.

Makeup gain: Once the dynamic range of a signal has been reduced, the overall signal can be increased (if desired) without causing clipping distortion. Check the compressor’s gain reduction meter and set the makeup gain at the average level shown on the meter.
Signal Routing II: Sends
A send (sometimes referred to as an auxiliary send) is an audio device that copies a signal or a portion of a signal from a track to a bus—an audio path that connects a destination to one or more sources. In this case, the destination is a processor and the sources are any tracks that need processing. Note that the signal path through the track is not interrupted by a send; instead, a user-defined portion of the track’s signal is copied to a bus. Multiple tracks can have a send set to the same bus in order to share the processor. This is optimal for delays and processor-intensive devices such as reverbs.
Pro Tools example:

1. 
   To create a send, click on a track send and set the output to the desired bus (or interface output if using an external processor)
   
   1. 
      Create sends on any additional tracks that are to share the processor and set to them to the same bus.
      
   2. 
      To create a send simultaneously on all tracks, Option-click a send and set it to the desired bus.
      
   3. 
      To name a send right-click the send and choose the rename option
      
2. 
   In order for the different tracks to get differing amounts of processing, the send on each track has a fader that allows the user to adjust the amount of signal that is copied to the bus. The more signal that is copied from the send to bus, the more obvious the effect will be.
   
3. 
   Create an Aux track (because plug-ins can only be placed on track inserts).
   
   1. 
      Set the Aux track input to the same bus as the Send
      
   2. 
      Place the desired processor on one of the Aux tracks inserts
      
4. 
   The Aux track fader functions as the master effect return control.
   
5. 
   Note that, when processing on inserts is referred to as series processing, the use of Sends is different. In this case the unprocessed (“dry”) signal is routed out the respective source track outputs. The signal gathered through the sends is processed by the signal processor inserted on the “return” aux track, which (in most cases) only returns 100% processed or “wet” signal. This is called parallel processing.
   

Example: Sends and Parallel Processing