Delay Line
Purpose
Delay Line devices implement an audio time delay. Delay Line devices are available with a single and multiple delay taps and with various maximum delay times. DSP resources are consumed in proportion to the number of delay taps and the maximum delay of the device even if none of the taps are set to the full delay time. Select the smallest delay line which satisfies the requirements of your application. The Delay Computer contains additional controls for automatically setting the delay time based on the physical location of the sound source and the locations of the speakers.
Controls
Bypass
Bypasses the delay line for all taps. The Input Level control is not bypassed. Setting all Tap Delay Times to 0 produces the same effect as activating Device Bypass.
Input Level
This controls the overall input level into the delay line.
Output Level
Allows control of the output level of each delay tap.
Tap Bypass
Bypasses the delay line for a single tap. The Input Level control remains in the signal path. Setting the Tap's Delay Time control to 0 produces the same effect as activating its Tap Bypass.
Tap Delay Time
Adjusts the delay time for a tap. Each delay tap operates independently. You do not need to be concerned about delay times crossing each other. Setting the delay time of a tap to 0 causes the delay line to be effectively bypassed for the tap.
Note: The delay time is rounded to an even multiple of the audio sampling period. If, for example, on a system running at a 32kHz sample rate, you Typed-in "50u", the system will respond with and set a delay time of "62.5u".
Additional 3D Delay Controls
Auto Calculate
Puts the delay device in Auto Calculate mode. When on, the Delay Time is set automatically based on the Position controls, the Listener Height control and the Extra Delay control. Adjusting a Delay Time control manually takes the device out of Auto Calculate mode. See how delays are computed for a description of how the delay time is set automatically.
Extra Delay
Indicates the extra delay to be added to the geometrically calculated delay time when the device is in Auto Calculate mode. See how delays are calculated for more information.
Feet/Meters
Switches the units displayed by the Position controls between feet and meters.
Listener Z
Indicates the height from the floor of the listeners head. For purposes of the delay calculation, the listener is assumed to be standing directly under the corresponding tap location. See how delays are calculated for more information.
Position X,Y,Z
Indicates the 3-dimensional position of the delay input and each of the delay taps.
The source X,Y,Z controls identify the physical position of the sound source. The tap X,Y,Z controls identify the physical location of the speaker that will be reproducing the signal coming from the corresponding delay tap. The listener of the sound coming from the speaker is assumed to be standing directly under the speaker, at a height given by the Listener Z control. See how delays are computed for a description of how these values are used by the device.
Delay Schematic
How Delays Are Computed
This paragraph describes how the 3D Delay device computes the Delay Time for a particular tap. First, the listener is assumed to be standing directly under the speaker position at a height given by the Listener Z parameter. The distance between the input location and the listeners head is computed and converted to time, this yields the direct delay time. Ignoring the Extra Delay parameter for a moment, we desire that the signal reproduced by the overhead speaker arrives at the listeners head with exactly the same delay as the direct signal path. The distance between the speaker and the listeners head is computed by subtracting the Listener Z position from the Speaker Z Position and converting this distance to time, this yields the speaker delay time. The Tap Delay Time is then set to the direct delay time minus the speaker delay time. In practice, one may not want the direct signal and the reproduced signal to arrive at the listeners ear at exactly the same time, but prefers the reproduced signal to arrive slightly later. This is the purpose of the Extra Delay control, to add additional delay to the geometrically computed delay to assure that the direct signal arrives first.
Delay Line Advanced Topic
The Deluxe Delay Line device is constructed of a Meter, a Strings algorithm, and a Delay Algorithm. The number of taps of the Delay algorithm and the maximum delay time of the algorithm are determined by arguments on the Algorithm String. The Algorithm String of the Delay Line has the following form.
DELAY A B
Where A is the number of delay taps. The legal range is 1 to 32. Values greater than 8 are not recommended because they can cause system inefficiency. And B is the maximum delay time. If units are not specified, this value is assumed to be in seconds. Typically the delay is specified in milliseconds by appending ms to the value. The minimum legal value is 1ms. The maximum value is dependent on sample rate, but 500ms is a safe maximum that will work at all standard sample rates. We do not recommend using delays greater than 200ms because you risk exhausting a DSP chips memory capacity before its processing capacity is exhausted, which results in an inefficient system that typically requires more hardware to run. Longer delays can be created efficiently by wiring multiple shorter delays in series if necessary.
Example
"Delay 4 125ms" creates a 4 tap delay with a 125 millisecond maximum delay.