Automatic Gain Control (AGC) Use in Lighting Equipment

Automatic Gain Control Use in Lighting Equipment

SN3 Innovations, LLC

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. Primary Contact: (603)505-5963 www.sn3innovations.com Legal Notice The information contained in this document represents the current view of SN3 Innovations, LLC on the issues discussed as of the date of publication. Because SN3 Innovations LLC must respond to changing market conditions, it should not be interpreted to be a commitment on the part of SN3 Innovations, LLC, and SN3 Innovations, LLC cannot guarantee the accuracy of any information presented after the date of publication. This White Paper is for informational purposes only. SN3 INNOVATIONS, LLC MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS DOCUMENT. Complying with all applicable copyright laws is the responsibility of the user. Without limiting the rights under copyright, no part of this document may be reproduced, stored in or introduced into a retrieval system, or transmitted in any form or by any means (electronic, mechanical, photocopying, recording, or otherwise), or for any purpose, without the express written permission of SN3 Innovations, LLC. SN3 Innovations, LLC may have patents, patent applications, trademarks, copyrights, or other intellectual property rights covering subject matter in this document. Except as expressly provided in any written license agreement from SN3 Innovations, LLC, the furnishing of this document does not give you any license to these patents, trademarks, copyrights, or other intellectual property. © 2015 SN3 Innovations, LLC. All rights reserved. SN3 Innovations, LLC, The Diamond Series, are trademarks of SN3 Innovations, LLC All other trademarks are property of their respective owners.

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.

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

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

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!

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 sensitivity knob accomplishes this task. The obvious downside to this method is that manual adjustment would be required every time the device is moved in relation to the speakers. This can be avoided with the proper implementation of an AGC block. Properly designed, the AGC will maintain an adequate signal level, despite the location of the lighting device in relation to the audio source, for optimal effects triggering.

AUTOMATIC GAIN CONTROL (AGC) USE IN LIGHTING EQUIPMENT AUGUST 2015 Implementing a Proper AGC Tailoring the AGC block for lighting entertainment purposes requires quite a considerable amount of design challenges stemming from high level architectural decisions all the way down to the circuit implementation level. Keeping this discussion focused on the architectural level, we can expand on the block diagram discussed early on. How do we improve on this? For those audiophiles out there, you’ll be more than familiar with the following two terms commonly associated with the dynamic properties of AGC use:

1. Attack Time : How fast the signal gain decreases 2. Decay Time : How fast the signal gain increases

Let's put these terms into perspective. If our output signal drops below our desired set-point then the AGC's job is to amplify the microphone input signal and raise our output back to the desired level. How quickly the AGC increases its gain setting is controlled by the Decay Time. Likewise, how quickly the AGC lowers its gain setting after the output rises above the desired set-point is controlled by the Attack Time.

Optimally configuring these parameters is a task that requires a great deal of trial and error. There are certain design guidelines to follow for audio specific applications where high fidelity is of great concern. However, for lighting entertainment applications our one and only goal is finding those discernible dynamic alterations in the audio signal to trigger effects on. This requirement leads to different Attack/Decay times than those required in audio applications. In fact, for lighting applications it is actually optimal to alter the Attack/Decay times in real time based on the dynamic properties of the music. This intelligence creates a much more sophisticated control block in our AGC model and leads to an improvement in lighting effects triggering.

AUGUST 2015 AUTOMATIC GAIN CONTROL (AGC) USE IN LIGHTING EQUIPMENT

If we put all of this together we can complete our sophisticated AGC block. The slight alteration in our Variable Gain Stage shows separate Coarse and Fine gain amplifiers. This structure is used to provide very fine gain granularity over a very large dynamic range. To put it simply, with this improved Variable Gain Stage, the AGC has the ability to fine tune its gain settings to hone in on the desired output level with improved efficiency. Now that we have our finalized AGC architecture what do we do? We use it! All SN3 Innovations, LLC lighting entertainment devices include this improved AGC circuit. So why don’t we compare the performance of the SN3 Innovations, LLC implementation to that of your standard lighting entertainment device! First, let’s take a look at the standard microphone amplification implementation used in the majority of DMX Lighting Entertainment devices on the market.

AUTOMATIC GAIN CONTROL (AGC) USE IN LIGHTING EQUIPMENT AUGUST 2015 Typical Microphone Amplifier in DMX Lighting Equipment The microphone amplification circuit implemented in most of the popular brand products in the market utilize a very similar technique. Mentioned earlier, this implementation does not include an AGC circuit. Instead, a manual variable gain adjustment circuit is utilized, where the manual adjustment is accomplished by a potentiometer identified as the sensitivity control knob. Granted, the details involved in low level circuit analysis is out of context for this white paper but it warrants a quick discussion in this case. The circuit shown is taken directly from a DMX Lighting unit, manufactured by an extremely well known company. We won’t mention any names here but if you’ve been around the lighting entertainment industry at all over the past decade you will be more than familiar with the name. It’s also important to note that this circuit is not unique to this device as it is replicated and used without much modification in more units than we can count! The operational amplifier (U1) in this circuit is configured as a differentiator with a varying pole location caused by the combination of C2 and our sensitivity control potentiometer R3. In most practical applications, this differentiator implementation wouldn't suffice for the following reasons:

1. The input impedance decreases with increasing frequency causing potential high frequency noise problems. 2. The lower and upper 3dB cutoff frequencies vary with changes in sensitivity settings (variations in resistance R3). 3. The upper frequency roll-off is not a result of a properly implemented and controlled pole. Instead it is an artifact of the open loop gain of the op amp. 4. The noise gain frequency response varies with changes in sensitivity level. At certain sensitivity settings the phase margin is borderline resulting in a marginally stable circuit. Analysis and simulation shows a worst case phase margin of 33° which would be frowned upon by any electrical engineer who follows good design practice.

The details involved with these potential pitfalls can fill a textbook so instead of getting into the nitty gritty we will focus on the most widely understood concept of this circuit: gain adjustment.

What happens as the user adjusts the sensitivity knob?

AUGUST 2015 AUTOMATIC GAIN CONTROL (AGC) USE IN LIGHTING EQUIPMENT As the user adjusts the sensitivity knob, the observed center frequency of the band pass filter along with the gain, changes. To be more specific, as the sensitivity is increased, the center frequency decreases, and vice versa.

What can we take away from this image? As we stated, when the user manually increases the sensitivity we see a shift in frequency response to the left. This is most certainly an undesirable consequence of this circuit implementation and offers no benefits. A more desirable implementation would have been to permanently fix the center frequency but allow the user to vary the gain with the potentiometer. Correcting the other design deficiencies hinted at earlier would also be nice but we’ll give them a little slack here! This variable frequency and gain response will in fact manifest itself in real time operation. For the common user it would be difficult to identify this specific non-ideal behavior while witnessing the lighting unit operate at a venue. A common complaint may be that the lighting unit doesn’t sync up properly with the audio or it seems to respond to sound differently under varying sensitive settings and speaker locations. Having a manual adjustment requirement could become quite a nuisance for the average user with this type of amplifier. To really drive this home let’s compare some real-time behavior of this common audio amplifier implementation to that of the AGC method included in SN3 Innovations, LLC’s products.

AUTOMATIC GAIN CONTROL (AGC) USE IN LIGHTING EQUIPMENT AUGUST 2015 SN3 Innovations, LLC vs The Competition In order to truly understand the benefits of a properly configured AGC for microphone amplification in lighting equipment, we need to take a look at the real-time behavior of this circuit while playing some music. With all the recent information we went over it’s easy to lose focus and forget the primary purpose of this AGC implementation so let’s recap. What are we looking for in real-time operation? We would like to see the AGC circuit maintaining a pre-defined average output level despite variations in the input signal. To go a little further, we’d like to also be able to easily identify dynamic changes in the audio signal for proper effect triggering. This latter requirement is accomplished with properly configured Attack/Decay time parameters. Enough analytical talk! How do we make this comparison? Simple…we place down one of SN3’s Diamond Series advanced entertainment lighting devices next to the typical DMX LED device we have been referencing. Next, we play some music at different sound levels and observe the output of the microphone amplifier block in each device simultaneously. To maintain consistency, we will set the sensitivity knob on the competitor’s DMX LED device to mid-level and will leave it there for the duration of this test. Understand that at a wedding, club, dance, or any venue where your lighting devices are in use, you will likely not have the ability to constantly adjust the microphone sensitivity. As a DJ, a host, or a guest yourself, you won’t have this time at your disposal so our experiment is a very realistic demonstration. We will use two separate audio samples: Audio Sample #1 will consist of a very basic drum line consisting of bass drum kicks, snare, and hi-hats. Audio Sample #2 will consist of a very intense electronic rhythmic line. This sample is consistent with the style normally used in modern drum & bass or heavy techno/dance music played by popular DJ’s at dance clubs. Both audio samples will be played at a low/moderate volume level as well as a very loud level in order to test the dynamic properties of the microphone amplifier blocks.

AUGUST 2015 AUTOMATIC GAIN CONTROL (AGC) USE IN LIGHTING EQUIPMENT Experiment #1: Audio Sample #1 – Played at a Low/Moderate Volume Our first test already shows a significant functional difference between the two devices. The Diamond Series device from SN3 Innovations, LLC displays much sharper peaks on the bass drum kicks as well as noticeable signal peaks during snare hits. The competitor’s DMX LED device does show noticeable peaks during the bass drum kicks but minimal reaction otherwise. Let’s see what happens when we significantly increase the volume.

Experiment #2: Audio Sample #1 – Played at a High Volume Significantly increasing the volume and playing the same audio sample highlights some very important results. You’ll notice that the Diamond Series device from SN3 Innovations, LLC produces a very similar output signal as that shown in Experiment #1. Both the bass drum kicks and snare hits remain easily identifiable. As you can imagine, triggering the lighting effects to sync with the audio signal is very simple here despite the volume of the music. This is what we want! If we look at the output signal on the competitor’s device you’ll notice a significant change from Experiment #1. The bass drum kicks produce an output signal amplitude over 200% compared to what we witnessed while playing the audio sample at a low volume. Additionally, we can now notice the snare hits in the signal waveform. This significant difference in output signal will undoubtedly cause the effects to behave differently. In other words, while playing the exact same music but at different volume levels, the competitor’s lighting device will sync up to the audio source differently. This is not what we want. Experiment #3: Audio Sample #2 – Played at a Low/Moderate Volume Playing a serious bass intensive audio sample shows a much different signal waveform. At a very low/moderate volume level you can easily pick out the necessary trigger points in both devices. In this audio clip, the bass hits are actually sustained for a short duration between drops. This sustained sound can easily be seen in the signal from the Diamond Series device. The competitor’s DMX LED device doesn’t show this sustained bass signal very well. The reason the SN3 Innovations, LLC device is able to really bring that portion of the signal out at low volume levels is due to the optimized attack/delay times in the AGC circuit.

AUTOMATIC GAIN CONTROL (AGC) USE IN LIGHTING EQUIPMENT AUGUST 2015 Experiment #4: Audio Sample #2 – Played at a High Volume Increasing the volume substantially and playing our Audio Sample #2 shows similar results as our first two experiments. Once again, the Diamond Series device is able to maintain a very similar output signal despite significant changes in volume. The competitor’s device on the other hand, shows a very significant difference. The benefits of an AGC microphone amplifier is really starting to show itself here. To take this one step further let’s increase the volume even more and zoom in on a single bass hit.

Experiment #5: Audio Sample #2 – Played at a VERY High Volume For this final test we’re approaching decibel levels similar to that found in dance clubs and wedding venues where the DJ gets a little too much control over the sound system! Not surprisingly, you’ll notice a very clean output signal in the Diamond Series device with a similar amplitude compared to our previous experiments. For the competitor’s DMX LED device we notice some problems. The output signal here is clearly saturating and causing noticeable distortion. Without constantly controlling that sensitivity knob, the competitor’s units don’t stand much chance in maintaining consistency.

AUGUST 2015 AUTOMATIC GAIN CONTROL (AGC) USE IN LIGHTING EQUIPMENT Conclusion We’ve evaluated a typical microphone amplifier implementation used throughout the lighting industry. Due to the number of inefficiencies, SN3 Innovations, LLC determined that a new approach to microphone amplification would be required to improve customer satisfaction. As a result, an AGC microphone amplifier was implemented resulting in a fully automated solution requiring no manual sensitivity control. For traveling DJ’s and mobile users who don’t have the luxury of permanently installing their lighting gear at a venue with a fixed sound system, this implementation is a life saver. The development and use of this properly configured AGC circuit is just one of the many ways SN3 Innovations, LLC is simplifying the use of lighting equipment. All devices in the Diamond Series line of products from SN3 Innovations, LLC includes the AGC circuit discussed in this white paper. For customer inquiries, technical questions, or specific questions related to this white paper please don’t hesitate to contact us. www.sn3innovations.com [email protected] (603)505-5963

AUTOMATIC GAIN CONTROL (AGC) USE IN LIGHTING EQUIPMENT AUGUST 2015