Automatic Gain Control Use in Lighting Equipment SN3 Innovations, LLC Automatic Gain Control (AGC) Use in Lighting Equipment White Paper Date: August 2015 Acknowledgements Initiated and released by the SN3 Innovations, LLC team, this document was developed with support from across the company and in direct collaboration with the following: Key Contributors Greg Notaro, MSEE (SN3) Technical Reviewers T. Scott Notaro, MS, MBA (SN3) Doug Notaro, PhD (SN3) Feedback Please send comments or suggestions about this document to the SN3 Innovations, LLC Team feedback alias mailto:[email protected] SN3 Innovations, LLC designs advanced entertainment lighting equipment for use by a broad array of customers. Ease-of-use is the primary focal point in the company’s development strategies and is achieved by incorporating novel design concepts and technically advanced solutions that alleviate operational challenges associated with current products on the market. 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SN3 Innovations, LLC, The Diamond Series, are trademarks of SN3 Innovations, LLC All other trademarks are property of their respective owners. 2 AUGUST 2015 AUTOMATIC GAIN CONTROL (AGC) USE IN LIGHTING EQUIPMENT Preface The lighting entertainment industry is flooded with DMX capable LED products that operate under very similar design methodologies. Comparing similar product types amongst the different big name manufacturer’s results in an abundance of similarities with regards to electrical design. One particular example is that of audio amplification. The traditional method utilized in almost all currently available products consists of a variable gain amplifier stage with a sensitivity knob linked to a potentiometer. This technique requires the user to manually adjust the gain of the amplifier in order for the lighting effects to trigger off of the music properly. SN3 Innovations, LLC takes a different approach to this design problem by implementing a circuit referred to as an Automatic Gain Control amplifier. This technique alleviates the required manual adjustment of the traditional approach allowing the user to experience a properly synchronized light show without intervention. Comparing and contrasting these two amplification methods will show the benefits of an Automatic Gain Control amplifier for lighting entertainment purposes. 3 AUTOMATIC GAIN CONTROL (AGC) USE IN LIGHTING EQUIPMENT AUGUST 2015 Revision and Signoff Sheet Change Record Date Author Version Change reference 7/27/2015 Greg Notaro .1 Initial draft for review/discussion 1.0 Updated with additional content and feedback from review comments Reviewers Name Version approved Position Date Autumn Ossai .1 Autumn Ossai 1.0 CEO T.Scott Notaro 1.0 CE0 Distribution / Signoff Name Position T. Scott Notaro CEO Doug Notaro Co-Owner Greg Notaro Co-Owner 4 AUGUST 2015 AUTOMATIC GAIN CONTROL (AGC) USE IN LIGHTING EQUIPMENT Table of Contents What is Automatic Gain Control? ............................................................................... 6 Why Do We Care? ................................................................................................... 7 Implementing a Proper AGC ..................................................................................... 8 Typical Microphone Amplifier in DMX Lighting Equipment ............................................. 10 SN3 Innovations, LLC vs The Competition ................................................................. 12 Experiment #1: Audio Sample #1 – Played at a Low/Moderate Volume ...................... 13 Experiment #2: Audio Sample #1 – Played at a High Volume .................................... 13 Experiment #3: Audio Sample #2 – Played at a Low/Moderate Volume ...................... 13 Experiment #4: Audio Sample #2 – Played at a High Volume .................................... 14 Experiment #5: Audio Sample #2 – Played at a VERY High Volume ........................... 14 Conclusion ............................................................................................................ 15 5 AUTOMATIC GAIN CONTROL (AGC) USE IN LIGHTING EQUIPMENT AUGUST 2015 What is Automatic Gain Control? Automatic Gain Control (AGC) is a concept used in the Electrical Engineering world to describe the functionality of a very specific type of amplification stage. This self-regulating amplification stage is an electronic circuit constructed in a close-loop fashion with the purpose of maintaining a controlled signal level at a designated output node, despite variations in signal level at the input. In other words, if the input signal is lower than the desired set-point, the AGC stage will apply a calculated amount of amplification to the signal in order to boost it up. Conversely, if the input signal is higher than the desired set-point, the AGC stage will attenuate the signal accordingly. In order to construct a proper AGC circuit we must introduce a few key building blocks. From our previous definition, you’ll recall that we need a circuit element which is capable of not only applying amplification but also attenuation to our input signal. The building block in question is known as a Variable Gain Amplifier (VGA). Self-explanatory right? So far so good! Now, building the actual VGA requires a multitude of trade-offs, design constraints, cost/benefit analysis, simulation work, math, more math, etc. Those details are out of the context of this white paper so we’ll stick to the basics. All we need to know here is that the VGA is a circuit which can amplify or attenuate an input signal in response to a control signal provided by an external block. What is this control signal you might ask? Good question! The control signal, labeled “control” in the provided diagram, closes our loop and communicates the desired amplification setting to our VGA stage. In order to generate this control signal there are two important pieces of information that we require: 1. What is the current level of our output signal? a. This is determined by the Average Level Detector circuit block. This block will create a DC voltage which is proportional to the average level of the output signal. 2. What is the desired output level? a. This is a DC voltage representing the desired average level of our output signal. If the Average Level Detector produces a DC voltage equal to that of our Desired Output Level signal, then our AGC block did its job and all is good in the world! Our control signal is simply the difference between 1 and 2: Control (V) = Desired Output Level Signal (V) – Average Level Detector Signal (V) Applying this control signal to our VGA closes the loop and completes our AGC block! 6 AUGUST 2015 AUTOMATIC GAIN CONTROL (AGC) USE IN LIGHTING EQUIPMENT Why Do We Care? Unless you’re an Electrical Engineer you’re probably asking yourself: Why do I care? What does AGC have to do with lighting equipment? To be quite honest, if we’re looking at typical DMX capable lighting equipment on the market today from popular manufacturers then the answer is quite simple: We don’t care! AGC doesn’t exist in most of these products. Instead, these products rely on a manual mode of Variable Gain adjustment. You know that microphone “sensitivity” adjustment knob on the back panel of your lighting unit? Well, there’s the source of your manual mode of Variable Gain Adjustment. So much for being “Automatic!” However, this doesn’t answer our question so let’s put on the breaks a little...we are getting ahead of ourselves. So why do we care about AGC in lighting entertainment? In order to successfully trigger lighting effects to a music source you need to either program the scenes yourself or allow the device to do this for you. For ease-of-use, we would like the device to be able to handle this job on its own. Just about all lighting entertainment equipment on the market contains a built-in microphone for this purpose. Now, in order for the electronics to successfully analyze the music, the microphone signal must be amplified to a level adequate for deciphering these trigger points. Traditionally, manual adjustment via the