7.3.10. IMBE/AMBE Vocoder

This page allows you to configure your recorder to use internal or external IMBE/AMBE Vocoders to decode IMBE/AMBE encoded audio, such as P25 or DMR, etc. If your NexLog DX-Series™ recorder is fitted with an internal DVSI Vocoder or two, the Internal Vocoder Resources field will show the number available. Check the box to enable these.

If you are using an external DVSI Net-2000 Vocoder IPs or external EFJohnson JEM II Vocoder IPs, you can configure as many as needed, one IP address per line.

7.3.10.1. Background Vocoding

As with previous releases, when recording P25 Audio from sources that provide audio in their native codec (IMBE or AMBE), the audio is stored on the recorder’s hard drives in the same native format it was received in. When playback or export is selected from MediaWorks DX™ or the front panel, the configured vocoding resources (External DVSI Net-2000 boxes, EFJohnson JEM II servers, or DVSI Vocoding hardware installed internally to the NexLog DX-Series™), are used to decode the audio on demand.

The advantage of this strategy is that AMBE and IMBE are very efficient at compressing audio, so much less disk space is needed to store the data. On the other hand, the disadvantage is that the amount of required vocoding hardware resources scales linearly with the number of users who are doing playback or export at any one time. Exports of large numbers of files will be slow, generally no faster than 4x real time (e.g. an hour of calls will require at least 15 minutes to export.) And finally, during times when those resources are not being used, they are idle.

IMBE/AMBE Vocoders Configuration

Fig. 7.43 IMBE/AMBE Vocoders Configuration

The Background Vocoding feature, if enabled, will use those idle resources to convert saved IMBE/AMBE calls on disk to a data format that can be played back without using the vocoding resources at playback time (G.726/16, G.726/32, and G.711 are supported). The advantage of having files pre-converted is that playback and export do not require the vocoder resources and will be just as fast as export/playback of other audio formats. The disadvantage of background vocoding, is that the data formats will require more space on disk than the native IMBE/AMBE data would have.

With the feature enabled, whenever a configured vocoding resource is idle, it will be put to work loading files from the disk, transcoding them, and then resaving them. When you go to playback/export a call, if it has already been vocoded, no vocoder resources will be required at playback and playback/export will be much faster.

The Channel Range to Decode option defaults to checking all calls on all channels, but you can configure this to only evaluate and vocode calls coming in on specific physical channel IDs. You can enter ranges with hyphens or delimit with commas; for example, if you want to decode channels 2,3,4,5,6,17,18,19, you could enter 2-6,17-19.