Telos One Mix-Minus

[ptfigg]

The Digital Hybrid

Before we discuss the implementation of the Telos One Digital Hybrid, it is important to understand what this device is designed to do. The digital hybrid in general uses digital technology to subtract the send audio form the return audio during a telephone conversation. Specifically, the send signal is the host audio sent out from the console, and the return or receive audio is the caller audio fed back into the console. This allows both participants to converse seamlessly. The program host speaks into the studio mic and monitors the caller's response via headphones. The caller hears the host through their handset just as if a typical phone connection and conversation were taking place. Finally. the entire conversation can be routed to a set of outputs on the console for subsequent recording.

Recording

Recording options vary depending on the specific work-flow. For example: a stand-alone DAT deck or a solid state CF recorder can receive the console output for subsequent recording. In our example, let us assume that the main output from the console will feed a set of available inputs on an audio interface. The signal will then be digitized and sent to a computer running compatible multi-track recording software. Examples include Digital Performer, Logic Pro and ProTools. This is a common method that will provide essential flexibility in terms of capturing the host and the caller on independent tracks.

Hybrid I/O

As illustrated in the diagram above, there are 3 XLR jacks available on the back of the Telos One. We will be working with the standard input [far left] and the standard output [far right]. The middle jack option, or the AUX/MIX OUT provides additional flexibility if necessary. For example: if you require a mix of the conversation, specifically one channel of audio that contains both the host and caller, simply set the push-button switch to the required position. This jack can also act as a second output that essentially matches the caller output from the main out jack.

Please be advised that balanced cables are required. In most cases an XLR male to 1/4" male [balanced], and an XLR female to 1/4" male [balanced] are common considerations. Last but not least, you will need to connect a standard telco feed to the line jack. A typical passive phone jack is provided as well. The hybrid does not need to be powered on in order to send and receive telephone calls as normal.

Mix Minus

Objectives: Allow the Telos One to receive an incoming telephone call. Speak to the incoming caller on the studio mic. Monitor [hear] the caller's responses through studio headphones.

In order to accomplish this we implement a mix minus bus using an Auxiliary Send Bus available on a mixer. Aux buses tap a portion of a channel signal and routes that signal to an output located somewhere on the console. Under normal circumstances we would also require the signal to be fed back into the console via Auxiliary Returns. A typical example would include sending your mic channel audio out to an external signal processing device and have it subsequently returned for proprietary use. However in this case, our only concern is a one directional output path that will provide the host audio to the caller.

It is important at this stage to set the input on the back of the Telos One to line with the push button switch. The next step is to connect the Aux Send 1 output located on your console to the input on the Telos One. For this initial process of configuration I suggest that you set the mic channel fader to unity gain, and set the Aux Send 1 bus level on this channel to the 12 o'clock position. The host audio is now available to the caller.

Connect the main output on the back of the Telos One to the right jack of a line input channel on your console. I suggest setting the channel fader at unity here for initial configuration purposes as well. Do not ignore the Aux Send Bus level on this channel! In fact, it must be off. Any increase in the send level will route the caller's audio back to the hybrid input. Remember - only the host audio needs to be sent to the the hybrid.

Notice the Send Master level setting area in the console diagram. This level parameter controls all referenced levels across an entire bus on a cumulative basis. Each channel can be set to a specific level, and the master send controls the entire bus unniversally. Set this to 12 o'clock as well for our initial configuration.

Below the Send Master parameter you will notice a Pre-Post switch. In the pre position, the Aux bus levels are placed before the specific channel fader. In the post position, the Aux bus levels are placed after the specific channel fader.The Telos One manual specifically states "the sources that feed the mix minus bus should be pre-fader so that they are always feeding the hybrid, and so the operators cannot upset the send level". In my opinion, this setting is entirely up to the engineer. Personally I prefer the post fader setting. This gives me dynamic control when accessing the channel fader if an adjustment is necessary during a live session.

Pan and Prepare

Notice the pan-pot [balance] settings on the individual input channels in the diagram. By hard-panning the channels left and right respectively, the conversation audio can be segregated, or routed to individual inputs on your audio interface. This will provide essential customization within your DAW or multi-track recording application. Simply associate each channel with an independent track within your application and record as needed.

Final Thoughts

I provided general recommendations in terms of levels solely for initial configuration purposes. Please keep in mind that proper level management, including send levels, individual channel levels, master output levels, gain trim parameters and hybrid trims are imperative in order to achieve optimum results. Success will require trial, error, and experimentation on a proprietary basis.

Lastly, there are specific parameters and settings located on the front of the Telos One. They are in fact the source of a future article. Keep in mind that proper configuration is required at this level as well.

-ptfigg. ny

10.14.2006

©Copyright GigaVox Media ... P.Figgiani Msc 2007