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From There to Hear: Audio Over IP
Another well-known maker of IP codecs is Musicam, and its Suprima has had some recent improvements. Suprima is a 1RU, two-channel, full-duplex IP codec that has some unique features. It has balanced analog inputs and outputs, as well as AES ins and outs (will sync externally or generate its own clock). It has a single Ethernet port that is used for control and the actual stream (TCP or UDP); control is done via its internal Web server. The Suprima also supports multicast over compatible networks. Seven GPIO connections are included, and it will support an auxiliary data stream if operating in MPEG mode or standard Apt-X modes. The unit will support linear PCM and codecs supported are G.711, G.722, Musicam ISO MPEG1/2 L2, ISO MPEG1/2 L3, MPEG2/4 AAC-LC, MPEG4 AAC-LD, MPEG4 AAC-HE, Standard and Enhanced Apt-x(64,128kb/s; mono, dual, j-stereo). It will also support Dolby E when the AES input is used, with the codec set in transparent mode.
The device has seen recent improvements to its network management, including better FEC, jitter and buffer control. Also, the Suprima has its own methodology for using two IP links, called Solid Stream. This feature permits two Suprimas to connect via two different IP data paths. Finally, the Suprima can pull down audio files from a USB stick, and play them out in the event that it detects an IP connection failure.
Another established player in IP codecs is Worldcast Systems, which took over the APT line of hardware codecs several years ago. It makes several IP codec products, but the one I chose to highlight is the Horizon NextGen (previous page). This is also a 1RU, two-channel, full-duplex codec that features dual-Ethernet connections on its rear apron, one of which can be used for a LAN connection while the other is used for the streaming output. IP transport is accomplished via RTP/UDP or SIP/SDP, and not surprisingly, Horizon Nextgen is fully N/ACIP compliant. The device supports unicast, multiple-unicast and multicast (assuming a compatible network).
Audio inputs and outputs are accomplished via XLR connectors, analog or AES. Four optically coupled inputs, along with four relay outputs, are included for GPIO (DB15 connector).
In addition to linear PCM, the unit supports Enhanced Apt-x. As an option, you can include MPEG 4 HE-AAC versions 1 and 2.
Control can be done from the front panel LCD screen and keypad or via its network connection using the Worldcast Network management software, or simply via its embedded webserver. SNMP support is provided as well.
SureStream is the name of the Worldcast feature that allows the Horizon NextGen to make user of two IP links to the far end device, thus providing extra reliability, especially over the public Internet. If you intend to use an IP codec over a trunked system (i.e., multiple VLANs) you'll be interested to know that the Horizon NextGen supports VLAN tagging.
- continued on page 4
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