New Media Technology Omnia ONE Multicast manual Final Limit, Important Note

Final Limit

Drive

The Drive control controls the depth of final limiting. The amount of gain-reduction occurring in the final limiter can be monitored on the Process metering bargraph screen. Note, however, that this meter cannot show extremely fast action in the limiter, so your ear must be the final judge.

LPF Freq (Low Pass Filter Frequency)

This is a key control and is used for matching the audio bandwidth of the processed audio to the bitrate of a following codec. Setting this control to the proper bandwidth for the codec’s settings will ensure minimal side effects and aliasing distortion products from the codec process. The available settings are: 4kHz, 6kHz, 8kHz, 10kHz, 13kHz, 16kHz and 22kHz. These are the frequencies at which the low pass filter reaches a minimum of 100dB of attenuation.

One of the most important features that an audio processor for codec provisioning must have is a high quality, low overshoot low pass filter after the final peak control stage. OmniaONE Multicast offers this feature as a low pass output filter that can be set to one of seven stop band frequencies. Each of the filters possess minimal passband ripple and are phase linear below cutoff. Response in the filter stop bands is greater than -100dB.

The following chart recommends low pass filter settings that, in our experience, best complement the AAC+SBR, MP3, and Windows Media (WMA) codecs. They were derived through thousands of hours of critical listening and we feel they are very good starting points for achieving the best overall sound although you may use other settings that you feel are more appropriate for your particular codec application.

AAC/SBR	Output LPF	MP3	Output LPF	WMA	Output LPF
24kbps	8kHz	24kbps	6kHz	24kbps	5kHz - 6kHz
32kbps	10kHz	32kbps	6kHz	32kbps	8kHz
48kbps	13kHz – 16kHz	48kbps	8kHz – 10kHz	48kbps	10kHz – 13kHz
64kbps	16kHz	64kbps	10kHz – 16kHz64kbps		13kHz – 16kHz

!!!--- IMPORTANT NOTE ---!!!

Always set the low pass filter frequency so that it is at or below half the sampling frequency of the encoder. This must be done in order to comply with the Nyquist Theorem1. Doing so will achieve the highest perceived audio quality.

OmniaONE Multicast - Use and Operation Manual – Version 0.90

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