The bit Drive software includes a powerful tool for analyzing input signals, a multi-channel input analyzer called electrical RTA. The electrical RTA is displayed within the Input EQ window, and displays the effects of the Input EQ and Input Delay settings in real time. Using the electrical RTA and a full-range mono (correlated) pink noise signal, it is possible to test for frequency response, amplitude, delay, polarity, and phase.
The Input RTA does not measure phase, rather it allows various channels to be temporarily summed together and displays the result. To determine if two channels are in phase with each other, the user can sum them together: if the content of the two channels are the same amplitude, and are in phase with each other, the resulting measurement will increase +6dB. Any change less than +6dB in the sum indicates some degree of phase misalignment at that frequency. For more information on using this technique, see Audison’s Technical Documents and educational information.
The Input RTA display is a live measurement, and the sampling takes place after the Input EQ and Input Delay processing occurs. This allows the user to correct the signals as desired, in a very short amount of time!
The user can select the INPUTS window and then press the Input equalizer button shown below to open the tool.
The following window will appear:
The window is composed as follows:
Input EQ
12-band parametric Input Equalizer for each channel. This equalizer is Parametric in operation. Each band can be configured as a Peak EQ filter, a Low- or High-Frequency shelf filter, a notch filter, a 1st-order phase-inverting all-pass filter, or a 2nd order phase inverting all-pass filter.
Gain, Center Frequency, and Bandwidth values can be adjusted either with the virtual slider or by clicking in the text field and inserting the exact value by keyboard.When a band is selected, the corresponding point on the graph will be highlighted.
The filter types available are:
Peak EQ filter: the user can select Gain, Center Frequency (any frequency between 20 - 20kHz), and Bandwidth (Q). +/- 12dB of gain is available. The Q value can be set between 0.5 and 16.
Shelf filter (Low or High): the user can select Gain, Center Frequency (limited to the lower or higher end of the frequency range, respectively), and Bandwidth (Q) from 0.5 to 1.41
Notch filter:the user can select Center Frequency and Bandwidth. The Q value is variable from 1.44 to 16. Gain is not available;
1st-order All-Pass filter: the user can select Center Frequency. A 1st- order all-pass filter gradually changes the phase 180° above a given frequency. Above that frequency, the phase will transition from normal to 180° inverted. Gain and Bandwidth are not available.;
2nd-order All-Pass filter: the user can select Center Frequency and Bandwidth. Gain is not available.
A 2nd-order all-pass filter gradually changes the phase 360°. At the Center Frequency of a 2nd-order all-pass filter, the phase value has been changed 180° (the change is halfway to completion). As the phase approached 360°, the signal is essentially back in phase with the signal below the 2nd-order all-pass filter. The Bandwidth (Q) controls the width of the filter, or, how gradually the phase changes from 0° to 360°.
Note: It can be useful to think of a 2nd-order All-Pass filter as changing the phase from 0° to 180° at the Center Frequency, and then back to 0°. While this is not a strictly accurate description from a technical perspective, it is a good functional description.
Input delay
Allows each Input Channel to be delayed individually. The user can change by:
◼︎ Click in the text field, and Insert the value using the keyboard
◼︎ Clicking the + and – buttons (fine set), to increment/decrement the delay by steps of ±0.01 ms:
To check for time delays in the source:
- play track 4 – Pink Noise and select the Input channel concerned
- add it with the channel of the same Front if present
(for example if you want to check channel 1 – Front Left Tw, add it with channel 3 – Front Left Wf).
a. If the electrical sum increases by +6dB at all frequencies, the two channels are aligned in time and phase and no further control is necessary.
b. if the resulting response has deep holes present at periodic intervals, a "comb filter", this indicates that a time delay is in use in the Source for one of these channels.
- To correct a comb filter trend, open the Delays tab in the lower-left corner of the RTA window. Add delay to the far channel (in LHD vehicles, this is usually the even channel). The comb filter should move to the right of the RTA graph, affecting higher and higher frequencies. Increase the delay until the response is flat.
- If the comb filter starts decreasing as you add delay to one channel, reset that channel's delay to "0 ms" and start adding the delay to the other channel you are adding instead.
- The goal is to get a flat response to all frequencies.
Example of "comb filter" due to time delays inserted in the source.
Channel view selection
Select the input and/or output channels to show in the monitor. The input channels are always white text, while the output channel labels follow the same colors applied in the main window.
Note: If multiple Input channels are selected, the analyzer screen will display the electrical sum of the selected channels. If an Input Channel and an Output channel are selected at the same time, they are displayed independently.
Electrical Real-Time Analyzer Display
Shows the signals selected in the previous point. The input sum graph is shown with white color, while the sum of the outputs is light blue.
By pressing the right arrow the user can open the monitor settings. Once these settings are changed, the change is retained and will be unchanged the next time the bit Drive software is opened.
It is possible to adjust:
◼︎ The resolution (that is, the number of Bands displayed)
1/3 = 30 bands, 1/6 = 60 bands, 1/12 = 120 bands
◼︎ Sampling average (very short, short, normal, long); (Normal or Long is recommended)
◼︎ Maximum and Minimum Graph scale limits These change the vertical resolution of the display.
If too wide a range is displayed, changes in amplitude can be difficult to discern.
EXAMPLE 1: one input channel.
EXAMPLE 2: electrical sum of input channels
EXAMPLE 3: one output channel
EXAMPLE 4: electrical sum of output channels
EXAMPLE 5: electrical sum of input channels (yellow) and electrical sum of output channels (blue)