AoIP_Gateway_Configuration-7
Keywords: NQ-GA400P

Setting DSP Parameters

When you select DSP (Digital Signal Processing) from the appliance’s web UI, the DSP page appears. This page presents a mixing board interface, allowing you to monitor, control, and perform DSP operations on the signals of the input and output channels.

Note: Digital Signal Processing (DSP) refers to the digital operations that are performed to modify or control the digital signal.

Figure 1. DSP Page

Note: The terms analog input and analog output will be used to refer to the electrical signals on the physical analog ports (e.g., from a microphone and to an amplifier) while network send and network receive will refer to the digital streams that are sent and received over the network.

The DSP page displays a mixing board console containing two input strips and two output strips. The input strips accept the analog inputs from the line input connectors and—after gain adjustments, analog-to-digital conversion, and DSP enhancements—send the digital network send over the network. The output strips accept the digital network receive from the network and—after DSP enhancements, digital-to-analog conversion, and gain adjustments—send the analog output to the line output connectors.

Each strip controls the audio signal for a given channel, providing muting, gain adjustments, signal processing, and more. Signal processing includes traditional audio processing, such as hi/low-pass filters (output), limiters (input), and parametric EQs (output).

This console can be used to do the following:

View Signal indicators for each channel.

Adjust the Input Gain level for each analog input signal.

Adjust the Input 1/2 level for each network send signal.

Adjust the Output 1/2 level for each analog output signal.

Apply DSP effects to the digital signals of both the input and output channels.

Selecting the DSP Features menu at the top-right corner of a channel displays a menu of DSP features for that channel. Each channel, both input and output, has its own associated menu, and the corresponding DSP features will be applied to the signal for that particular channel.

The various mixer controls, as well as the DSP features available via the DSP Features menu, are briefly described in the following table and will be discussed in more detail in subsequent sections.

Note: The DSP page (including the mixing board and other DSP pages) can only be used by one browser session at a time. If another session is already connected and using this DSP page, the mixing board displayed will be disabled.

Table 11. DSP Page

Save Settings to Server | Backs up the DSP settings to the server. If this device is later replaced or reset to factory defaults, these DSP settings can be restored when the new device is “swapped” for the old on the Nyquist server. Note: This button appears on each DSP feature page.
Mute | Silences the audio for the selected channel.
DSP Features button | Presents a menu of DSP features that can be applied to the corresponding channel.
Channel Fader | Adjusts the channel volume level in 1 dB increments.
Signal LED | Illuminates when a signal is present.
IN VU meter | Indicates the strength of the analog input signal.
OUT VU meter | Indicates the strength of the network send signal.
Input Gain | Adjusts the strength of the analog input signal.

The DSP features that can be applied to a channel, accessible through the DSP Features menu, are described in the following table.

Table 12. DSP Features

High/Low Pass (Output only) | Filters out frequencies in the input signal that are above and below specified high and low cutoff frequencies.
Limiter (Input only) | Prevents a signal from exceeding a certain preset maximum level.
Parametric EQ (Output only) | Uses a center/primary frequency to all tailoring of the frequency content of an audio signal.
Settings | Allows you to provide names and colors for the input and output channels.
Signal Present | Allows you to configure the threshold level and duration that a signal must reach before the Signal LED will be activated for this channel.
Reset button | Present on almost all DSP screens other than the main mixer, this button will reset the DSP settings to the displayed feature’s default setting.

See also:

"Adjusting Input Gain” on page 22

"Signal Indicators” on page 21

"Muting a Channel"

"Adjusting Volume Levels"

Setting the Channel Level

The channel level control is a channel fader, which is adjusted in 1-dB increments and controls the output level for the channel. The channel levels can range from −60 to +12 dB. If you place the mouse over the fader, the numerical value of the level appears.

Adjusting Volume Levels

The channel fader control can be used to adjust the channel’s output level in 1-dB increments between −60 and +12 dB. The overall adjusted output level of the channel signal can be viewed on the OUT VU meter, marked in 2-dB increments between −60 and 0 dB.

Tip:​For best results, adjust input signal levels until you have a strong signal (i.e., within the green and yellow areas on the meter), then adjust the final output levels using the DSP Outputs controls.

To adjust the channel volume level:

1​On the appliance Web UI’s main page, select DSP.

2​Use the channel’s fader to adjust the volume level.

Knob Adjustments

Many DSP controls use knobs to adjust one or more settings. The value of a knob can be adjusted in one of two ways:

1​Click the knob control, hold the mouse button down, and drag the mouse up or down to increase or decrease the value.

2​Double-click the knob, type a value into the resulting popup, and click the Save button.

Signal Indicators

Each input channel has signal indicators and two vertical volume unit (VU) meters, labeled “IN” and “OUT”.

The green input signal LED(s) automatically illuminates when a signal is being received.

The “IN” VU meter indicates the strength of the channel’s input signal (after gain adjustments), while the “OUT” VU meter indicates the strength of the channel’s output signal. The VU meter not only illuminates green, yellow, or red (depending on the signal level), but also has a scale ranging from −60 to 0 dB to indicate the actual signal level.

Muting a Channel

You can mute a channel to cut off an audio signal and stop the input signal from being sent to the output channel. Note the input signal will still be visible on the IN meter, but the OUT meter will show that nothing is being forwarded to the output channel.

To mute a channel:

1​On the appliance Web UI’s main page, select DSP.

2​Click the Mute button for the channel that you want to silence.
The Mute button will illuminate red. You can click the Mute button again to unmute the channel.

Adjusting Input Gain

Because input signal levels can vary greatly based on the attached device, you will want to adjust the Input Gain for a channel to ensure the input signal level is high enough to use, but not so high that it sounds distorted. The input signal level can be viewed on the “IN” VU meter and adjusted using the Input Gain knob.

Tip:​Typically, a good input signal will vary between the high green and low yellow areas of the VU meter, but your ears should be the ultimate judge of a good signal. Remember, the purpose of the Input Gain is to adjust the strength of the input signal, not the volume of the final output signal.

See also:

"Muting a Channel"

"Adjusting Volume Levels"

Troubleshooting Gain Structure

Channel faders should be set to 0 dB (unity gain) during the channel-level setup procedure.

The optimal operational range of the Input Gain control knob is from about 9 o’clock to 2 o'clock.

If Channel Clipping Occurs

If the signal is clipping or producing audible distortion, the gain is too high. Reduce the Input Gain knob by turning the knob counterclockwise until the clipping and distortion have been eliminated.

Also, make sure that the Input Gain is set within the optimal range between the 0 and −20 dB positions on the gain control knob.

If Channel Volume Is Too Low

If the channel fader volume control must be set above the +6 dB position to provide adequate volume, the Input Gain setting is too low. Set the channel level fader to 0, turn the Input Gain knob to the 1 o'clock position, and increase the Input Gain by turning the knob clockwise until clipping occurs or the VU meter’s signal level is between −10 dB and −3 dB. Then, adjust the Input Gain to a setting just below the clipping level.

If Channel Volume Is Too High

If a channel is not clipping but the channel fader level control must be set below the −20 dB position to achieve the proper volume level, the Input Gain control setting is too high. Set the channel fader to the 0 dB position and adjust the Input Gain control knob until the desired volume level is achieved. Reduce the Input Gain by turning the knob counterclockwise.

High/Low Pass

High-pass filters allow signals that are higher than the specified frequency and attenuate signals that are lower. Low-pass filters allow signals that are lower than the specified frequency and attenuate signals that are higher. When combined, they are known as a band-pass filter.

You can specify the range of frequencies that will pass through the high-pass and low-pass filters and select the type of filter that is used through the channel’s High/Low Pass drop-down menu option.

Figure 11. High/Low Pass Parameters

To adjust the high/low pass parameters for a channel:

1​On the appliance Web UI’s main page, select DSP.

2​Select the Menu button for the channel.

3​From the drop-down menu, select High/Low Pass.

Note: If you want to return to the factory settings, select the Reset icon that appears in the right corner.

4​Set the parameters described in the following table:

Table 13. High/Low Pass Parameters

High-Pass (Low Cut) This feature helps eliminate low-frequency noise (signals of 100 Hz and below, such as background rumble from ventilation systems, etc.).
Enable | Enables or disables the High-Pass filter.
Frequency | Set the cutoff frequency. You can adjust the frequency by moving the knob (click and move up or down) or by double-clicking the knob and typing the frequency. When typing the frequency, only numeric values from 20 Hz to 20,000 Hz can be entered. The high-pass filter attenuates content below this frequency and lets frequencies above this cutoff frequency pass through the filter.
Type | Available filter types are: Linkwitz-Riley (12, 24, 36, and 48 dB per octave) Butterworth (6, 12, 18, 24, 30, 36, 42, and 48 dB per octave) Bessel (12, 18, and 24 dB per octave) Note: The term “dB per octave” describes how steeply frequencies below the selected cutoff frequency are attenuated. For example, if the cutoff frequency is 100 Hz and the filter type specifies 12 dB per octave, a 50-Hz signal (i.e., one octave lower) will be attenuated by 12 dB and a 25-Hz signal (i.e., two octaves lower) will be attenuated by an additional 12 dB.
Low-Pass (High Cut) This feature helps eliminate high-frequency noise (signals of 8000 Hz and above) such as background hiss and sibilance (excessive "S" in vocals, etc.).
Enable | Enables or disables the Low-Pass filter.
Frequency | Set the cutoff frequency. You can adjust the frequencies by moving the knob (click and move up or down) or by double-clicking the knob and typing the frequency. When typing the frequency, only numeric values from 20 Hz to 20,000 Hz can be entered. The low-pass filter attenuates content above this frequency and lets frequencies below this cutoff frequency pass through the filter.
Type | Available filter types are: Linkwitz-Riley (12, 24, 36, and 48 dB per octave) Butterworth (6, 12, 18, 24, 30, 36, 42, and 48 dB per octave) Bessel (12, 18, and 24 dB per octave) Note: The term “dB per octave” describes how steeply frequencies above the selected cutoff frequency are attenuated. For example, if the cutoff frequency is 8,000 Hz and the filter type specifies 12 dB per octave, a 16,000-Hz signal (i.e., one octave higher) will be attenuated by 12 dB and a 32,000-Hz signal (i.e., two octaves higher) will be attenuated by an additional 12 dB.

Limiter

A limiter is a compressor with a high slope (i.e., attack) that is used to prevent a signal from exceeding a set decibel level. Limiters are used as safeguards against signal clipping.

Limiter parameters are set per channel.

Figure 12. Limiter Settings

To adjust the limiter settings for a channel:

1​On the appliance Web UI’s main page, select DSP.

2​Select the Menu button for the channel or select the Menu button for the Output.

3​From the drop-down menu, select Limiter.

Note: If you want to return to the factory settings, select the Reset icon that appears in the right corner.

4​Adjust the following settings as needed:

Table 14. Limiter Settings

Threshold | Sets the signal level at which the limiter is triggered. Any signal exceeding this threshold will be compressed to this level. The range is −24 to +24 dB.
Decay | Sets the rate for turn off of the limiter after the signal is below the threshold. Decay range is 5 to 2300 milliseconds.
RMSTC (Root Mean Square Time Constant) | Sets how fast the limiter reacts to a signal that has exceeded the threshold. RMSTC range is 50 to 10000 dB/sec.

Parametric EQ

A parametric equalizer is a multi-band variable equalizer that allows control of frequency amplitude (boost/cut), center frequency, and frequency bandwidth, or Q.

Figure 13. Parametric Equalizer Settings

The parametric equalizer settings for your device allows you to adjust the Q and gain for five separate frequencies, which then become plot points on the screen’s graph.

To adjust the parametric equalizer settings for a channel:

1​On the appliance Web UI’s main page, select DSP.

2​Select the Menu button for the channel.

3​From the drop-down menu, select Parametric EQ.

Note: If you want to return to the factory settings, select the Reset icon that appears in the right corner.

4​Adjust frequencies as desired, ensuring the Enable LEDs are green for each selected frequency. You can adjust the frequencies by moving the Freq knob or by double-clicking the knob and typing the frequency. When typing the frequency, only numeric values from 20 to 20,000 can be entered.

5​Make desired Q adjustments by adjusting knob (or double-clicking and typing the desired adjustment). Q can be from 0.1 to 20 and sets how wide to either side of the selected frequency the adjacent frequencies are affected.

Q is the Quality or Quality Factor, which refers to the bandwidth of one band of a parametric equalizer. Q is calculated by dividing the center frequency in Hz by the width of the boost or cut zone, +3 dB or −3 dB above or below 0 dB.

6​For each frequency, use the Gain knob or double-click the knob and type the gain to either boost (turn up) or cut (turn down).

Gain knobs can be moved between +12 or −12 dB. By default, each knob is set at 0 dB, which means that no frequencies are being boosted or cut.

7​Select Save Settings to Server.

Settings

You can specify custom names and colors for each of the input and output channels. This allows you to customize the appearance of the mixer board.

Figure 14. Settings Parameters

To adjust the settings for a channel:

1​On the appliance Web UI’s main page, select DSP.

2​Select the Menu button for the channel.

3​From the drop-down menu, select Settings.

Note: If you want to return to the factory settings, select the Reset icon that appears in the right corner.

4​For each channel, type the name that you want to display for the channel.

5​For each channel, select a color that will be used to highlight the channel.

6​Select Save.

Signal Present

You can configure the threshold level that a signal must reach before the signal LED is lit, as well as how long the LED will remain lit. You can configure this for each channel.

Figure 15. Signal Present Parameters

To adjust the Signal Present settings for a channel:

1​On the appliance Web UI’s main page, select DSP.

2​Select the Menu button for the channel.

3​From the drop-down menu, select Signal Present.

Note: If you want to return to the factory settings, select the Reset icon that appears in the right corner.

4​Adjust the following settings as needed.

Table 15. Signal Present Parameters

Threshold | Sets the minimum level the signal must reach before the signal LED is illuminated. Threshold range is −144 to +24 dB.
Hold | Sets the minimum number of milliseconds that the signal LED will remain illuminated. Hold range is 2 to 200 milliseconds.