Adjusting and Normalizing the Output Level of the Audio Signal of the SL NEO Server

Functionality of SL NEO server software allows users to adjust the output level and normalize the output audio signal. The given functions are actual when forming SDI-signals with the embedded sound, and especially when forming IP/ASI transport streams, so as in the last case the possibility and expediency of installation of de-embedders/emdedders and hardware devices for audio processing is completely absent. Let’s consider the details of configuring the given functional at the server platform.

Adjusting the output audio level

Control of parameters is implemented from the control panel - Administrator Control Panel. Login to the console is implemented locally from the server, or from any machine in the network by the address http://server_ip:7901. You should login to the control console as an administrator.

  

After the login to the control console, choose Manage at the console menu. Choose the tab Video IO Boards, then move to editing the parameters of the appropriate Playout service. Find the field Base Audio Level in the field General and set the needed value in decibels, to increase or decrease the output audio level.

 

The function is applied to all audio tracks in the output audio signal of the chosen Playout service, the default value is 0 dB. The level regulator is placed in the final chain of the server audio-path.

 

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After the end of editing, you should press Apply in the upper section of the control console window. 

Normalization of the output audio level: compression and limitation

The function of normalizing the audio level is provided for manual and automatic import of media files to the SL NEO server storage. Besides, you can activate the built-in compressor/limiter (the function DRC - Dynamic Range Compression) for on-line post-processing the audio signals formed by the server.

 

With different audio levels in the played back files and signals that come to the server inputs, the software module Audio DRC (is placed in the output part of the server audio-path) increases or decreases the transfer ratio. Thus, the average output audio level is maintained unchangeable. The module Audio DRC works both with monophonic signals and multi-channel audio, it simultaneously processes up to sixteen audio channels within one output playout channel of the server.

 

Audio DRC works with all types of output signals and interfaces, supported by SL NEO servers: SD/HD SDI/HDMI, Audio Embedded, AES EBU, Analog Audio and with DVB IP/ASI - transport streams. Every output server channel has the possibility of individual configuring the parameters of its program compressor/limiter. 

 

Configuring the parameters for automated adjustment of the level is implemented from the control panel - Administrator Control Panel. Choose Manage in the console menu, then choose the output device for configuring: find the tab Video IO Boards, then move to editing the parameters of the appropriate Playout service.

 

a_level2.jpgActivate the parameter Enable DRC in the tab Audio DRC. In the field Level Detection set the type of triggering for the compressor:

 

Peak - triggering by the peak values of the level. This way is used for limitation, when you need to limit the peak values of the signal to a certain threshold.

 

RMS - triggering by the average value of the level. RMS-compressor can miss short peaks of a signal, with practically no decrease of the transfer ratio. RMS-method is oftener used in compressors for volume leveling, so as loudness is more connected with the mean-square capacity, than with the peak capacity.

 

Upper Treshold - the threshold of triggering the compressor by the dBFS scale, the value of the input level, exceeding of which makes the compressor to start weakening the signal (see the levels diagram). Selecting this parameter is traditionally used for “leveling” the formed program.

 

Lower Treshold - the threshold of triggering the compressor, the value of the input level, below which the compressor starts to amplify the signal. The given parameter can be useful in case, when you need to slightly “rise” the level in programs containing speech and dialogues.

 

Ratio - the ratio that defines the intensity of weakening (as in case with Upper Treshold) or amplifying (in case with Lower Treshold) of the output signal by the compressor when exceeding/understating the input level; is expressed in the format “x:1”. For example, if you set the ratio “2:1”, in case of exceeding the Upper Treshold by 10 dB, the compressor will weaken the “level of exceeding” by two times, to 5 dB.

 

Noise level - the threshold level of noise, below which the signal will not be exposed to changes with the selected mode Lower Treshold. 

 

The compressor doesn’t have adjustments for the parameters Attack time and Release timeAttack time shows how fast the audio signal should be scanned for taking into account the changes in the sound level. The set value of 200 ms is chosen as the most optimal one.

 

The parameter Release time - the time the compressor needs to return to the condition of regular gain, after the moment when the signal has fallen lower the inflection point. The selected value is the minimum possible one, it is about 5 ms.

 

The limiter is the same compressor with the selected value Upper Treshold, configured to strongly limit the output level when exceeding the input level: the ratio of the input signal to the output one begins from the value 8:1. When using more hard limitation, undesirable nonlinear distortions may appear in the output signal.

 

After the end of editing the parameters of the module Audio DRC, you should press Apply at the top part of the server control console, to save the implemented settings.

 

To appraise the work of the module Audio DRC in the mode RMS you can use the avi-file, containing fragments of a 1kHz signal with different levels (from -42 to 0 dBFS). The video contains the information about the current levels values in a file - measuring the audio level from the server output, you can appraise the degree of compression and correctness of settings.