Home / My Disclaimer / Who am I? / Search... / Sign in

// Sound

On Resonance

by Steve Syfuhs / October 10, 2012 01:34 AM

In Physics there is a term called resonance:

Resonance is the tendency of a system to oscillate at a greater amplitude at some frequencies than at others.

In other words, if energy is applied to something, that something will vibrate more or less depending on the frequency applied to it.

For example, consider a speaker.

A speaker produces sound by oscillating air around it. It does this by converting electrical energy into mechanical energy. The electrical signals cause something to vibrate, and that vibrating thing causes air to vibrate as well. Sound is the vibration of air back and forth at given frequencies.

Hearing is the ability to convert vibrating air to electrical signals that are interpreted by our brain. A speaker converts electrical signals to vibrating air, and our ears convert vibrating air to electrical signals.

Acoustic resonance is, simplistically, the energy of the air movement causing something else to oscillate a lot more than usual. This something else could be a piece of furniture, the housing of the speaker, or even a building. When the right frequency is applied, that thing will start vibrating. This frequency is called the resonant frequency. In fact, there are multiple frequencies that can have such an affect on a single thing, and most things have different resonant frequencies. A lot of times these frequencies are fairly low in the spectrum of human hearing.

This is observed daily. Consider an idiot driving down the street playing really loud boomy music. You can hear everything vibrating on their car. Everything is vibrating because the sound from the music is causing things on the car to resonate, and you can hear the vibrations because its causing air to move.

Resonance is an interesting thing. Especially at 2:30am on a Wednesday because your neighbor is being a jackass listening to really low, loud music which is causing the foundation of your building to vibrate ever so slightly enough to make noise.

But I digress.

Facts about Sound you Probably didn’t Know

by Steve Syfuhs / August 11, 2010 04:00 PM

The other day I kept hearing this noise from my neighbor.  I couldn’t quite figure it out, and naturally it was annoying.  I didn’t do anything about it, but it got me thinking about some random facts about sound and noise.

Medium

Velocity

(m/s)

(ft/s)

Aluminum

4877

16000

Brass

3475

11400

Brick

4176

13700

Concrete

3200 - 3600

10500 - 11800

Copper

3901

12800

Cork

366 - 518

1200 - 1700

Diamond

12000

39400

Glass

3962

13000

Glass, Pyrex

5640

18500

Gold

3240

10630

Hardwood

3962

13000

Iron

5130

16830

Lead

1158

3800

Lucite

2680

8790

Rubber

40 - 150

130 - 492

Steel

6100

20000

Water

1433

4700

Wood (hard)

3960

13000

Wood

3300 - 3600

10820 - 11810

  • The range of human hearing is 20 Hz – 20,000 Hz, however most people can only hear between 40 Hz – 16,000 Hz
  • All frequencies are not equal.  Our ears perceive certain frequencies to be louder than others (found at Wikipedia http://en.wikipedia.org/wiki/Equal-loudness_contour):

Lindos1.svg

  • Sound travels a smidge less than 1 foot per second at standard temperature and pressure.  Therefore if you need to place speakers in front of other speakers, you need to delay them based on distance… 40 feet = ~40ms of delay.
  • If a speaker is placed in front of another without a delay, the sound from the speaker farthest from you will sound similar to an echo.  This is called the Haas effect.  However, most people don’t notice this until there is a 40ms gap between sounds, or roughly 40 feet.  After about 40ms of delay, the intelligibility of the sound also decreases.  I.e. it starts to degrade the quality, and you start having trouble understanding what you hear.

Mostly useless facts, but they are fun to know.

Balanced Audio Connections

by Steve Syfuhs / January 31, 2009 04:00 PM

Someone once told me that a balanced audio connection works because of polarity. I wish I had a rolled up newspaper so I could swat him with it on the nose. Balanced systems are used to keep noise and interference out of systems. It is a common myth that balancing a system involves polarity. It does not. Polarity plays a part in keeping interference out, but the real reason balanced systems work has to do with impedance.

image

This type of connection is known as an unbalanced system. There is only one connection leaving the Op-Amp in device A. The second connection is ground. In device B the signal is brought in on one leg of the Op-Amp and the the second leg is a replica signal sourced to ground (or reference). In other words the signal is the same except opposite (polarity). There is absolutely nothing preventing noise and interference from entering this system.

image

This is a balanced input. Notice how the input connector has 3 connections instead of 2.

image

This a balanced output. Notice the 2 Op-Amps and 3 connections. The balanced system has both connections equally referenced to ground. How this prevents interference is an idea called Common-Mode Rejection (CMR). Because interference hits all three wires in a cable at once, they will all have an equal level of extra noise. It is voltage essentially. When the signal enters the Op-Amp at the input it looks at the ground line and sees what’s on it. It then compares what it sees on the two signal lines. It kicks out what all three have in common. Hence Common-Mode Rejection.

This is theory though. Not all inputs are perfect, and because all cables have something called cable capacitance, voltages differ minutely on each wire within the cable and the rejection doesn’t work as well as the theory states it should. But it still works pretty darn well. There is a whole science devoted to developing a standard for getting better CMR. One of my favorite resources is Jensen Transformers’ Bill Whitlock. He is a freakin genius. Here is his seminar handbook on balanced and unbalanced connections. This is where it all started making sense to me.

Enjoy!

Proper Podcasting Equipment

by Steve Syfuhs / January 24, 2009 04:00 PM

I am not a podcaster.  I do not think I have the voice for continued listening.  However, I am a sound guy, and I am anal about it.  I did a search online to find out what equipment is necessary for podcasting and every time I came back with:

  • Microphone
  • Pre-amp
  • Digital Recorder
  • PC Editing Software

For each item on this list I have heard some very disturbing suggestions for what type/brand to use.  I thought I would dispel some myths about each piece of hardware.

Microphone

Behringer is not a professional product line.  They say they are; they are NOT.  I said it, and I will say it again: Behringer does not make professional equipment.  No way, no how.  They market the products as professional equipment that all the big stars use, but in actual fact the equipment would never make it on a tour.  It can’t.  It’s not stable enough, and it’s not reliable enough.  It WILL break.

Enough ranting about that.  There are two main types of Microphones you will be dealing with when podcasting.  Dynamic and Condenser.  They both have their merits.  Dynamic microphones are usually cheaper because they are easier to make.  The sound quality is theoretically lesser than a Condenser Mic.  And a Dynamic Mic does not need an external power source.

Sound quality is always an issue when recording.  However, a podcast is 99% vocal.  At least on the recording side it is.  On the frequency spectrum vocals range between 80 Hz and 1100Hz.  You do not need a super-ultra-fantastic microphone for this job.  In some cases you do, but generally if that were the case you wouldn’t be reading this article – you would be talking to an audio recording professional.

You also have your choice between a Cardioid and an Omni-directional Mic.  An Omni-directional microphone will pick up sound from 360 degrees.  It’s great for dealing with multiple people talking at once, but horrible if you are talking in a loud environment.  A Cardioid (pronounced: car-dee-oid) microphone is directional.  It will pick up sound from a single direction, and is excellent if you are the only person talking in a very noisy environment.

My two cents: go talk to a sound guy directly and tell them what you are doing.  They will understand.  Brand-wise I like Shure and Sennheisser.  By all means contact me if you want more help.

Pre-amp

A pre-amp will do one of two things, but first I need to explain how a microphone works.  Essentially a microphone works by producing a very small electrical signal that is a representation of the sound hitting a membrane within the microphone capsule.  Different types of microphones (electret, condenser, dynamic, piezoelectric etc) capture and translate the frequency patterns differently.  The important thing to know is that the electrical signal coming out of the microphone is extremely low.

The voltage is so low that most recorders cannot handle the voltage.  They need more.  A pre-amp takes care of this problem.  It amplifies the signal just enough so the recorder can use it properly.  In some cases microphones need voltage going to them before they can actually produce a signal.  Condenser microphones are notorious for this.  The required voltage is called Phantom Power.  It’s a long winded explanation of what actually happens with the phantom power, but for all intensive purposes, the pre-amp will usually take care of the phantom power too.  This is definitely something you need to talk to a sound guy directly about.

Digital Recorder

I never got into digital recording, but just from basic analog to digital conversion theory, here are some thoughts:

  1. Get a recorder that converts to a lossless format.  .Wav files are the most standard.  When recording you want the highest possible quality available.
  2. Get a recorder that has a balanced audio input.  XLR is balanced.  Get a microphone that outputs through XLR, and a pre-amp that takes XLR and outputs XLR.  You will end up with better quality.  Balanced connections do wonders for interference.  It won’t remove interference already in the system, but it will prevent any other from getting in.
  3. Get one that is durable.  You will drop it.  You just will.

PC Editing Software

For editing the podcast you want a piece of software that can handle multiple tracks.  This allows you to layer chunks of audio without losing data.  It also gives you more wiggle room to move parts around.  I like Adobe Audition.  There are many others out there though.

Zune Player

by Steve Syfuhs / January 05, 2009 04:00 PM

At first I was a little skeptical at the quality of the Zune Player, as it’s basically in direct competition with Windows Media Player.  In retrospect, that’s probably what made it what is today.  It’s designed to sync the Zune media player, and it works very well as an alternative to Media Player.  There are a couple problems that I have with it though:

  • It’s a resource hog
  • It requires a good video card to show effects
  • It sorts things in weird ways when meta data is missing

The Zune Player is built on .NET.  It has a very big initial memory footprint.  It gets better as it settles into place.  My assumption is that it’s using WPF to make itself look pretty, and that’s where all the effects come from.  As a result some video cards aren’t capable of handling the effects renderings.  For instance, my laptop’s video card just dies when the effects are on.  Zune will turn them off if need be.  If the Album Artist meta tag is empty, Zune sticks “Various Artists” in place thereof.  Zune sorts based on Album Artist in the default view, so when I loaded my library into it, a whole whack of songs where under Various Artists, which isn’t all that useful.  With that being said, all the (legally) downloaded content had proper meta tags and were sorted perfectly.

However, with all the negatives, comes a few gems.  Sorting is a breeze.  Playlists are extremely easy to build.  Filtering works.  And it’s a really slick UI.

zune

I’m a little miffed the band image is pixilated, but all the extra info brought with it makes up completely.  Talk about slick.

zune2

It also makes decent random playlist decisions.  On the UI and UX side of things it gets the job done.  It’s pretty stable.  It hasn’t blown up on me yet.  I give it my approval.  Check it out: www.microsoft.com/zune.

What Makes us Want to Program? Part 2

by Steve Syfuhs / January 02, 2009 04:00 PM

In my previous post I started talking about part of my personal history with software development, and when QBasic got me hooked.  I ended the post talking about the move to Canada.  We arrived in Canada literally a week (7 days exactly) before Grade 9 started.  After getting enrolled in school, I tried to find something to keep my mind occupied.  It was either that or contemplate what Grade 9 would be like for someone who used to live 3000 miles away in another country.  And winter.  Still 4 months away, but definitely something I didn’t want to think about.  Being that we moved to a house in the country, I couldn’t just walk around town either.  Mental occupation was harder than I thought.

So what does a 14 year old boy, new to the country, living in the middle of nowhere, do to keep himself from going crazy?  Install Linux of course!  I needed something to keep my interest, as well as to keep the gears in my head moving.  If memory serves, I started out with a vanilla copy of Red Hat Linux.  It was pretty easy to install, but being new to the OS architecture, the device mapping was a little confusing.  After a couple months of studying the Linux architecture, I started writing shell scripts, and even delved into the source code.  After testing some minor modifications to different components I started to learn the basis for the C/C++ languages.  Imagine that, a 14 year old kid understanding the basis for C++.

While trying to keep my mind still occupied, I came across an interesting find: The National Security Agency’s Security Enhanced Linux Kernel.  If compiled and installed wrong, you will destroy the build.  Learned that the hard way…  And seeing as I couldn’t find a proper driver for my modem anyway, I gave up on Linux and moved back to XP.  Not that the internet was all that useful anyway; I was connecting at 28.8 half the time.

Going back to the image in Part 1, I met an interesting character in school.  He turned out to be one of my best friends, and fellow developers, Greg. We started working on some odd projects here and there in VB, until I was tasked with building a web store.  Since I had never actually brought HTML and Dev together, I was a little nervous about what I was getting myself into.  Going with what I knew well, I started in ASP with VB code.  This was not ASP.NET.  Earlier, I had said I never found VB all that intuitive as a language.  The syntax never really made sense to me.  So my friend suggested I take a look at PHP as an alternative.  I liked it.

PHP had the flow of C, and the usefulness of VB.  With PHP I got the store finished and launched.  The site worked great.  I was 15.

Once the first spring of my existence in Canada rolled around, a couple friends and I decided to start a band.  We sucked.  But seeing as one of the other members was Greg, we had an awesome website.  We had media streaming, custom modified forums, and full site statistics.  The statistics were built around the forum.  The site pulled data from recent posts, recent events, and recent user logins, and compared the data to the media streams.  We could see who was doing what.  Mind you, there was only about 50 people who loitered around the site, but the site was a great proof of concept for what we could do.

Following the demise of the band, Greg and I were invited to a Microsoft hosted event.  It was here that I fell in love with ASP.NET.  Which I will discuss in Part 3.

The Tragically Hip Media Player

by Steve Syfuhs / December 23, 2008 04:00 PM
It's not every day you come across a band that is willing to stream all of it's songs free of charge.  Especially at a fairly high bit rate.  Well it seems the Tragically Hip have decided to do so.
 
It's a little game changing actually.  The band has decided to let everyone and their mother listen to the music free, with no advertisements.  Mind you, you can't take it with you.  But there is nothing technical stopping you from recording the stream.  That was always the fear with online streaming that the Record Labels and the RIAA had.  I don't condone pirating, of anything, but I do believe in free arts.  So this is cool.  Especially because I like The Hip.
 
 
The Tragically Hip
 
 
It's also pretty straightforward to use. On the main page select all the songs you want in the playlist, and then click "Launch Music Player". Very intuitive.

// About

Steve is a renaissance kid when it comes to technology. He spends his time in the security stack.