SFL Real World testing of Ether Sound capability on Yamaha M7CL-ES

I hope you find this information helpfull.
We have some more ideas and developments around the use of ES in live applications comming soon.
I should have some very exciting stuff to show you in January!
mark at sflgroup.co.uk

Bench Testing the Line6 2.4 GHz XD-V70 Radio Mic System

Introduction

At SFL we are currently reviewing the radio systems at our disposal in the light of post 2012 digital switchover and the clearing of TV channel 69 (and other) bands.

Its is likely that we will want to replace with GB specific product from the likes of Shure and Sennheiser who both at the time of writing have convincing CH 38 / 39 /40 reaching equipment in the guise of UHF-R (Shure) and G3/300/500 (Sennheiser).

More is More

Any readers that have attempted good intermodulation free production planning with more than say 8 channels of radio and some IEM (In Ear Monitoring) thrown in for good measure will know that we exponentially require more UHF bandwidth as the number of systems increase.

So the idea that we can have "another world" up in the 2.4Ghz area to expand the radio system playground.... this can only be a good thing.

Line 6 make a nice looking 24 bit digital system working in the 2.4GHz area ( http://uk.line6.com/xd-v/ ). My job over the last day or so has been to evaluate it for our needs for general use and hire stock. The apparent advantages of such a system would be as follows:

• >115dB dynamic range with no companding (great for general accuracy and measurement applications)
• Great signal to noise performance
• License free operation
• Immune to issues of DSO leading up to 2012 and beyond
• 12 channel compatibility
• Integrated antenna distribution

Gain Brain

http://line6.com/media/pdf/Line%206%20Wireless%20microphones%20Whitepaper%20UK.pdf



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Testing for Headroom



The above white paper from line6 explains that with such huge dynamic range in play (>115dB) there is no need for gain trimming at the transmitter as we are used to doing with traditional systems to optimise signal to noise performance. Indeed the V70 hand held unit and V70L belt pack transmitter indeed have no gain trims either in the form of electronic pots of menu options.



The belt pack system on V70L is advertised as having a 6.5V Peak to Peak maximum sensitivity at 3% THD.


I measure 6V peak to be just before visible clipping on a scope at 1KHz. That compares well to the spec. I cannot measure THD, I just watch the scope!



Below Clipping



Opps.. Over!

You may be interested to know that the first LED on the audio meter (on the RX) comes on at -70dB below full scale (defined by me as 6V P2P). The last "maximum top of the scale LED" comes on at -30dB below full scale. Hence in now way is the top LED a peak LED.. it is 30dB below peak.

You may also like to know that a DPA mic on a suitable standard TA4 connector ("Shure Type") works out of the bag. Also a Beta 98 plugged in on a TA3 to TA4 converter lead works out of the bag.

I conclude that this thing has ample headroom. At 24bit sampling we should have >115dB of dynamic range. We could argue that there is at least 45dB of dynamic range under the first LED, 40dB covered by the set of audio LEDs (bottom to top) and 30dB above the top LED to clip.

If I take a DPA 4066 with max SPL of 144dB before clipping with 6mv/Pa sensitivity.
We know 1Pa=94dB SPL

Raise 94dB to peak SPL (144dB) is an increase of 50dB.

We need 50dB (this is based on 20Log, its a pressure... do you agree?) of headroom above 6mV (I think this is RMS). This is a hence multiply factor of Antilog (50/20) = 316

6mV * 316 = 1.90V approx (I will assume RMS)
1.90/0.707 converts to peak = 2.6
Double it for Peak to Peak = 5.2V

Hey presto the V70L has 6V Peak to peak in the bag. You can grab a DPA 4066... yell down it like a madman and have headroom. There is no need to gain trim.

How Flat is Flat?

Here I use TuningCapture to plot the frequency response and impulse response from a log sine chirp.

In this test I compare the signal through the V70L belt back and compare the performance to a piece of wire doing the same job!

The control trace is in yellow with the performance through the V70L in red. Notice the V70 has usable bandwidth from 20Hz to 16KHz within 2dB. You can also see that the latency through the system is fixed at 4ms. In spatial terms that's just over 1M of latency. Not worth a worry in my world.... just good to know what it is.

To be honest right now I cannot fault it. Next I need to test to see how nicely the system plays with computer wifi working alongside it but for now this system gets a big "PASS" from me.

Regards

Mark Payne