The author, with the C1141 in the rack.
Looking farther into 2010, there is little doubt that audio over IP will continue to grow in playing a key role in remote broadcasting, studio-to-transmitter links and studio-to-studio audio distribution.
The Mayah Communications C1141 makes all three of these applications possible. The C1141 IP/ISDN codec offers the user the choice of an ISDN codec with IP remote control for management, or a codec for both ISDN and IP.
Out of the box, the first thing that users will notice is the small size, just 1RU half rack. Users can add a lot of devices in a small footprint. Its size does not affect its ability to deliver quality audio and offers users a variety of I/O.
Looking at the front, the LCD display is bright and easy to read, and the four LED meters make it easy to monitor send and receive levels. A simple keypad with function/menu buttons, number pad and arrow selection keys round out the display. The C1141’s sister, the C1140, is identical other than lacking front-panel controls; it is designed for remote use.
The rear-panel audio interfaces include analog XLR in/out and AES/EBU in/out/sync along with Ethernet (10/100 baseT). For communications the C1141 is equipped with optical in/relay out, USB Type A and USB mini (currently inactive).
The C1141 (and C1140) also has a module with four ISDN BRI RJ-45 couplers occupying an expansion slot. (Note: other members of the C11 family include expansion slots for PC cards [e .g., Compact Flash and PCMCIA] and SD memory cards while modules for additional Ethernet or ASI are available for placement into the expansion slot holding the ISDN BRI module).
Algorithms supported are G.711, G.722, MPEG Layer II and Layer III, MPEG 4, AAC-ELD, HE-AAC v.2, PCM (16–24-bit), with apt-X/apt-X Enhanced and 4SB ADPCM as options.
Setup of the C1141 was fairly simple, but with any gear that employs an array of options, users are better off walking through the manual. Setup options can be found through the menu buttons on the front or via the Web remote control interface. I found the latter is significantly easier. After assigning the IP address components to the device and logging into the remote interface, configuration of the monitoring, transmission and play/record menus is effortless.
For testing purposes I chose to compare the ISDN connection vs. the IP connections. My first test case utilized ISDN for transmission. Audio was AES in/out and in both cases, IP was used for remote control via a Java applet. The far end of the connection was to another identical C1141. As with previous Mayah codecs, the ISDN interface is robust, and the processed audio is crisp, clean and highly intelligible at both ends. Connections were made using most of the popular ISDN algorithms L2, L3, G.722, G.711, and there was no noticeable latency.
The second test case utilized the IP interface. This test was far more expansive than one might first think. There are many competing factors that affect the output such as connection rates, jitter, pack loss, etc. I chose to evaluate the following algorithms, L2 mono, L3 stereo, AAC mono, AAC stereo, HE-AAC and HE-AAC v.2.
I experimented with a studio-to-studio set up using the two C1141 connected across a local area network. As I expected, I had mixed results.
At L2 mono 64 kbps, there was little audible latency or jitter, however as I sought to increase the bit rate to AAC stereo 128 kbps the latency and packet loss started to become apparent . Since this was a bidirectional signal, I really needed to be able to cut down on latency.
I was unable to determine if the delay was due to network congestion or latency due to the analog/digital conversions. If latency is not such a big issue, such as in the case of a studio-to-transmitter link, the user can increase the delay setting in the Ethernet parameters. The delay can be set up to 5,000 mS, so that if the packets aren’t received in the correct order, the buffer can delay the transmission so that correct ordering can be achieved. If possible for the user’s application, the delay buffer on the receiving codec should be larger than the average network jitter. In my case, my average network jitter was between 23 and 40, so I could choose to set my delay to the same or higher value.
For my testing purposes, however, I chose to disable AJC (automatic jitter compensation), and leave the delay set to 0.
For users unfamiliar with IP audio codecs, FEC (forward error correction) and AJC exist to help improve the transmission quality, but can also affect timing of the audio signal or packet. The AJC and FEC, when enabled, automatically adapt the stream to deliver continuous high-quality audio, despite a significant packet loss. So if you need IFB or a studio-to-studio bridge, you are better off reducing the IP overhead in favor of better communications, otherwise feel free to increase the delay, and send a higher bit rate stream.
Another nice feature that the C1141 employs is adaptive bit rates. Not only does this feature automatically configure the algorithms on each connection end, but it is constantly monitoring the stream to determine if a higher bit rate can be used.
For instance, in my testing I had the following bit rates established:
- – HE-AAC stereo 24 kbps actually yielded between 32 to 47 kbps on average
- – HE-AAC stereo 64 kbps actually yielded around 71 kbps
- – L3 stereo 64 kbps actually yielded 78 kbps
Further exploring the IP capabilities of the C1141, I sought to test the SIP functionality.
The C1141 employs both real-time transport protocol (RTP) and session initiation protocol (SIP), the latter enables the C1141 to make connections to other SIP-compatible codecs. This feature greatly simplifies remote broadcasting over IP, and enables users to add on SIP codecs without having to stick with the same brand to ensure connectivity.
Mayah C1141 IP/ISDN Codec Thumbs Up
- + Compact 1 RU half-rack size
- + Full-featured codec supporting both ISDN and IP audio (bidirectional)
- + Full-color LED VU in/out meters
- + Convenient front-panel connection status LEDs
- + Simple Web GUI for remote access and monitoring
- – A bit arduous to set up without Web GUI
For information, contact Mayah Communications in Washington at (360) 618-1474 or visit www.mayah.com. For the purpose of this review I was unable to obtain another branded SIP codec to test this feature. I was however able to test the SIP functionality of my two C1141s. Mayah provides an SIP account for every SIP enabled codec. This is basically there to test and try out the SIP functionality for free.
The setup of the SIP account is just as simple as assigning the IP address. Again, accessing the codec from the online Java applet is the simplest method to set up this service. Found on the same menu as the Ethernet settings, users can assign a server, and register their accounts. Once authenticated, a convenient SIP status light appears on the connection status lights, and also on the main LCD screen of the codec itself. Placing a call to the SIP server is essentially no different than dialing an IP address. SIP connections were made popular by VoIP applications, and because of their success in voice over IP, they work well to transport audio over the public Internet. Instead of configuring the IP address of a remote codec each time it moves to a different network or remote location, the SIP allows the codec to move around, and yet send and receive calls from any other SIP codec using its unique ID.
The Mayah Communications C1141 ISDN/IP audio codec worked well in a variety of testing scenarios. The C1141 includes a lot of features, and a substantial list of algorithms to satisfy basically any audio application. The ISDN is reliable and proven, but this device shines by adding on the advanced IP capabilities and SIP functionality. If you are new to IP audio, this device couldn’t be easier to configure.
It is important to remember, however, with any IP technology many of the characteristics of performance will weigh on the quality of the IP connection, bandwidth and quality of service settings. As I found, giving yourself adequate time to test, and try different combinations of settings will result in finding one or more setups that work well in your situation. Last, never be too prideful to ask your IT person for a little assistance.
Laura Mir, CBNT, has been a radio broadcast engineer for more than 10 years. She’s based in the Washington area.