Posted tagged ‘SIM3 Analyzer’

Off to Mexico for AES and SIM3 Training – Updated

April 25, 2010

I have been busy putting together new material for SIM 3 training, and AES seminar and the upcoming Broadway Sound Master Class. You have seen some of the work in progress below, but I have had to push to get things ready for showtime.  Sorry for the delay in getting more things posted and for my lateness in response to Goran. Just pushing it right now – LOTS of really good stuff coming- phase circles galore but priorities………..

AES Expo

I was invited to give a talk for the AES at the Sound Check Expo in Mexico City

This is a big audio trade show in Mexico City. Lots of  levels of gear mixed together: Pro Audio, Music Industry Audio, Guitars, Pianos, Disco lighting , and the most popular event was getting the autograph of a hot young girl singer. I am sorry but I never made it to the front of the line. :-(.

I did a talk for about 1.5 or  hours and it was like giving a speech at the United Nations. There was a faint spanish language echo in the room when I spoke, about 500 ms delayed. It was a translator in a booth at the rear and everybody in the audience was listening on headphones. Wow, this guy was fast – and good, because I even got a few laughs at my jokes. I remember doing a translated seminar once in China. 4 days without a single laugh – until I tripped and fell down on the stage – the crowd loved THAT!   OK back to Mexico. The lecture was very well attended and it was a great honor to have so many people there. We covered alot of interesting topics including subwoofers steering and fun stuff like that. I was told that this was the best attended training session of the convention (about 120 people) and that felt really good. If only I could have gotten the singer girl to join me on stage we would have REALLY filled up the place!

Here are two pics from the seminar. The first one shows me at the podium. I don’t remember the bubbles floating around the room, but you can see them in the picture. The second one shows the view in the room.

AES Sound Check Expo

SIM3 Seminar

 Next on the agenda was Meyer Sound Mexico where we held a SIM3 Training. It was the usual 4 day session, but in Mexico City the sessions are marathons. Typically we go from 10 am to 7pm, but two of the days we went past 9 pm. The Mexico city schools are some of the most interactive of all the schools I do. The students are sendiing up a constant stream of interesting and challenging questions and we cover SO MUCH material. Sometimes the order in which we cover them is a bit crazy, but we cover TONS of topics.

Working with me on this seminar was Oscar Barrientos and Mauricio Ramire(el Magu). These are expert teachers in their own right so it is great to have them to translate and enhance. My typical style, when doing a translated seminar, is to (try) keep my talking short, to make quick switches to the translators. With these guys, because they know the subject so well, they can follow the concepts and even expand on what I say when they move it into Spanish. This helps speed things along alot – because typically a translator has no audio knowledge, does not know the terms, and certainly does not know FFT analysis. (In Korea once we had a translator QUIT at lunch time the 1st day – because she was too humiliated by all the students telling her she was translating all the audio words wrong. A student, Sean Cho, took over the job and saved the seminar).

Most of the students had been to Magu’s and/or Oscar’s training courses before and a few (Eduardo Brewer from Venezuela and Jorge and Juan Carlos Yeppes) had even been to my course before. It is the ultimate honor for me to have engineers return to my course.  The advanced level of the students helped us to move along at a very fast pace.  I am always very grateful about the way i am treated in Mexico. They are SO GOOD to me.

I also had the honor of meeting Luis Pinzon. He is the only person I know with 3 copies of my book – 1st & 2nd edition ingles, and 1st edition espanol. I happily signed all 3 for him. I wish I had brought a Chinese version to give to him. That would have completed the set!  . Luis also gave me his cable checker – which is quite amazing.

I was taken to some really nice restaurants by Antonio Zacarias and also  we went for Tacos to El Charco – which I highly recommend.  Also went to a Chinese restaurant in a shopping mall near Meyer Sound Mexico – I DON’T recommend this place, unless you want to die.  Funny though ….A week later I had Mexican food in China – The Mexican food in China was better than the Chinese food in Mexico, but Mexican in Mexico and Chinese in China worked out the best.

So here are some photos from the Mexico seminar, taken by Eduardo and Hermes. I think I have the names right on the class photo – if not help me out please. Also if you have some others – please send them to me.

Thanks for inviting me to Mexico, and I hope I can come back soon —actually I WILL be back in Mexico this Novemeber – but it  a cruise vacation – so I won’t be working 🙂

Until next time,

Hasta luego y Buena Suerte

6o6

 
Mexico SIM3 Class 2010

6o6 is getting some hands on experienceNow we know who was reading email during class

Yes this is supposed to make sense..........

Magu, Oscar, Paco and 6o6

Eduardo, Magu, Hermes, 6o6, Oscar and the bald guy

6o6

A Concise Article on Cardioid Subwoofer Arrays – by Steve Bush

March 25, 2010

This article  Tech Talk: Building Directional Subwoofer Arrays

Working toward consistency. was posted just today on the ProSoundWeb by Steve Bush.

Well written, concise, plain English and NO MATH!

 (lo siento que no es Espanol pero tiene fotografias).

I need say no more.  Geez.  That was the easiest post I ever did!

6o6

Cardioid Subwoofer array in an arena

Interpreting Coherence on the FFT Analyzer

December 31, 2009

When we make the transition from the simplistic renderings of one-dimensional acoustical analysis, i.e: those that present amplitude only, we have several new traces to contend with. The most notable are phase and coherence. Phase is often minimally grasped and coherence even less so. These are both difficult because we don’t have simple mechanisms in our ear/brain system to detect them, especially when either of these functions varies with frequency (which is almost always the case).

Last week I received an interesting set of questions about coherence from Geoff Maurice of Brockville Ontario and I though it best to answer it here since others may share the interest and contribute to the discussion. What Geoff is looking for is coherence explained without going hard into the math, so here we go.

1) Coherence is a statistical metric: It monitors the extent of the variation in the data sampled. Therefore, first and foremost we must have multiple samples. In FFT terms this means were are “averaging” the data.  If we have at least two samples, we can statistically evalaute the averge amplitude and phase values and the deviation between the individual samples.  An average amplitude value of +6 dB could be the product of two nearly identical – or vastly different samples. The coherence value indicates (inversely) the extent of the devation between the average and the individual samples.  Low deviation= high coherence and vice versa

2) The deviations between the samples that degrade coherence can be EITHER amplitude or phase or BOTH. Most factors affect both. Examples of this are wind, ambient noise, reverberation, a change in a filter setting. 

3) There are some factors that degrade coherence continually and some that degrade it only for a limited time. Continual degradation is caused by  the summation of the original signal with a relatively short delayed copy (the most obvious example is an echo).  The comb filtering results in a series of peaks and dips in both amplitude AND coherence. Variable degradation comes from non-correlation sources such as ambient noise.

4) Geoff asks: what mechanism causes a complete cancellation to reduce the coherence.  This is an interesting one. A complete cancellation at a given frequency results from the  summation of equal level signals that 180 degrees apart. At the place where this occurs (our measurement mic) the original signal (the first arrival) is not audible since it has been neutralized by the reflection. Since our transfer function analyzer is looking to compare the original electronic signal to the acoustic arrival it finds the signal missing at the mic. This does mean there is silence at the mic. Far from it. Instead what we have is any and all other signals in that frequency range. Reflections from long ago, signals from other sources (stage, sound fx) and ambient noise.  All of these signals will have very poor correlation to the original electronic refernce signal. On the contrast side the same early reflection will make for excellent coherence at other frequencies where the late arrival falls 360 out of phase – which means it is “in phase” and will add to the original signal. Strong early reflections make for stable coherence – high AND low. 

5) Geoff asked about the relationship of the number of averages to the coherence value. The coh value is calculated from whatever quantity you choose. If the deviation percentage is the same over two samples as it is over 16 the coh value will be matched. In the case of SIM we use a coherence blanking function that screens data below a given threshold. THAT threshold varies with # of averages. Why?  If you have just two samples you have “he said/she said” – who is right?  (we know this but I am not saying) – so these two better match or we can not resolve it.  With 16 samples we have lots of data to work with. One or two can be far off and not pull the average down to far.  So we use a high threshold (90%) for 2 averages and a low threshold for blanking with 16 average (20%).

6) next Q was – would you call a coherence value of 50% accurate?    yes………and no. A coherence of any value can be accurate. 0% coherence is an accurate representation of all noise and no signal.  But I think where the question goes is: how much coherence is good enough to act on?  The answer here is the ultimate in sliding scale.  Grading a curve on a curve.  If I am measuring a frontfill speaker in the second row , 50% is a very poor value.  If measuring an array in the back of an arena 50% is a great number. For me looking at coherence trends is more helpful than considering a particular number. A drop to 50% in an area where others are much higher gets my attention as would a drop to 20% where the median is 50% . A rise to 50 % where most are very low would also get my attention. Why is this range getting through, while others aren’t?

There is a start on this subject. Anyone with thoughts is invited to comment

6o6