Chladni Plates

Mojo Goro

Ernst Chladni  was a German physicist and musician, most known for the Chladni Plates – an experiment which still looks intriguing to most of the people. This experiment is a good and beautiful way of visualizing the nodes and antinodes on a vibrating surface. Originally this experiment was obtained with a metal plate with some sand on it that is driven into various resonant states with the use of a violin bow. The plate itself like everything in the physical world would have a certain resonant frequency, and when the frequency of the vibrations matches or is proportional the resonant one, these interesting shapes as in the picture below would be formed by the sand.

Chladni Plates patterns for different frequencies

You can actually watch a modern recreation of the original experiment on youtube:

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Seven Nation Army

Amazing! MSC Magnifica [1] plays “Seven Nation Army” song (White Stripes) during the 825th Hamburg Port Anniversary celebrations [2] on May 9th 2014 [3]:
http://youtu.be/sTlTxFio6DY

 

References

[1] MSC Magnifica. Retrieved 14 May, 2014, from http://en.wikipedia.org/wiki/MSC_Magnifica

[2] 825th Hamburg Port Anniversary celebrations. Retrieved 14 May, 2014, from http://www.hamburg.de/hafengeburtstag-english/

[3] Cruise Ship playing Seven Nation Army. Retrieved 14 May, 2014, from http://youtu.be/sTlTxFio6DY


Air beds enhance Eurovision lyrics

The Sound Blog

A few years ago I saw acoustician Niels Adelman-Larsen present a new design of acoustic absorber at a scientific conference. His early prototypes were actually air beds. Now, Niels’ has moved on from the camping store, to commercialise the technology, and these absorbers are playing a vital role in ensuring that this year’s Boom Bang-A-Bangs at the Eurovision can be clearly heard.

This year’s Eurovision Song Contest is being held in the enormous, tinpot shipyard in Copenhagen. Left untreated, the sound would rattle around the room for ages creating a muddy sound. The way a sound lingers in a large space is evaluated via the reverberation time, a measure of how long it takes sound to wither away to silence. In a classical concert hall, the reverberation time is typically about 2 seconds, in the Eurovision venue before treatment it was 13 seconds and so completely unsuitable for Hard Rock Hallelujah.

Photo: Niels Werner Adelman-Larsen, Flex Acoustics Photo: Niels Werner Adelman-Larsen, Flex Acoustics

The solution to…

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Mixing console construction and installation

Found this awesome article (with loads of pictures) about the construction and the installation of API Legacy Plus 96 mixing console in famous Blackbird Studios:

http://www.apiaudio.com/Photos/Blackbird/Install/photolog.html [1]

 

And here is a Blackbird Studio tour with John McBride [2]:

 

References

[1] API Legacy Plus construction and install. Retrieved 6 May, 2014, from http://www.apiaudio.com/Photos/Blackbird/Install/photolog.html

[2] Blackbird Studio Tour with John McBride. Retrieved 6 May, 2014, from https://www.youtube.com/watch?v=YWesb1MaEMI

 


Funny Leadership Lesson

Funny Leadership Lesson [1]:

 

Referneces:

[1] First Follower: Leadership Lessons from Dancing Guy. Retrieved 4 May, 2014, from http://youtu.be/fW8amMCVAJQ


Digital Audio Basics

Oh, how I wish I would have seen these Xiph.Org [1] videos about 3 years ago:

Episode 1 [2]:

 

Episode 2 [3]:

 

They are also available for download:
http://xiph.org/video/vid1.shtml
http://xiph.org/video/vid2.shtml

 

References

[1] Xiph.Org. Retrieved 1 May, 2014, from http://xiph.org/

[2] Xiph.Org – A Digital Media Primer For Geeks (episode 1). Retrieved 1 May, 2014, from http://youtu.be/Ny7krNFAD1s

[3] Xiph.Org – Digital Show & Tell (episode 2). Retrieved 1 May, 2014, from http://youtu.be/d7kJdFGH-WI


Digital Audio Latency

I recently wrote a post about the amp simulations and how good they have gotten in past 6 years. And I mentioned a small problem that all computer based systems have – latency. In this post I will go into what impact it has and why is it important to keep it low, when you are using virtual instruments, tracking songs with plugins from your DAW or just jamming using amp simulators on your computer.

Often you see that manufacturers say their gear is zero latency or near zero latency. And that is true. But that’s only true, when the interface is in standalone mode or it does not route input signal through the computer, because input signal is directly routed back to the output. Or, if audio interface has an on-board DSP chip, signal is processed within the interface and AD/DA converters become the main reason for the delay (there is also very small delay due to on-board DSP). But nowadays converters are very fast, so interface with on-board DSP chip has a near zero latency.

But, when you are routing signals through the computer, the main source of latency usually is the computer itself. Without going into much detail what happens under the hood – it takes time to run your signal through the computer and process it. This PreSonus article [1] briefly describes the process. You can have the fastest converters in the world and still have a noticeable latency, if your computer is not set up right. You are often given the control over the sample rate and the buffer size, but even with the best possible settings there will still be some latency, which you do not have control over and which often is not reported by the system. That is the latency that is introduced by the drivers. And some manufacturers employ “hidden” buffers to ensure smooth playback as mentioned in this SoundOnSound article [2]. But the good news are that if total latency (also called RTL – round trip latency) does not go over about 10 – 12 ms, you are OK as long as you are not a singer, who is very sensitive to the latency.

Signal going through analogue circuitry is nearly instant because electrical signals travel through the wire about 2/3 of the speed of light (299 792 458 m/s) which is way, way faster than the speed of sound (343 m/s in normal conditions). And that is why big PA systems often need delay units for speakers that are placed further away from the stage. Latency of 6 ms is equal to your speaker being about 2.06 m away from your ear, which is approximately how far my cabinet usually is from me, when I play. I can easily live with latencies up to about 10 ms (which is equivalent to distance of 3.43 m). After that it starts to get distracting because you can feel the lag between strumming the guitar and the arriving sound. For singers it is crucial to have almost no latency as the mouth is not that far from ears. Plus sound travels as vibrations through your head from the vocal chords to the hearing system faster than through the air from mouth to eardrum. Which is why people, who are not used to the sound of their recorded voice, feel like they sound different (due to combination of signals), but that is a topic for another post.

Some audio system setup comparisons were done by Vin Curigliano from AAVIM Technology and are posted in his DAW Bench website [3], which is a great source of information. You can use RTL Utility [4] to measure your total system delay.

I am using TC Electronic Konnekt 6 (Firewire 400) audio interface and here are my results:

Sample Rates (Hz)                                       Buffer Sizes (samples)

                                         512                    256                  128                  64                 32
44100                           28.686 ms     16.888 ms     11.271 ms     8.180 ms    6.918 ms
48000                           26.350 ms    15.684 ms     10.350 ms    7.691 ms    6.350 ms
96000                           14.327 ms     8.998 ms        6.327 ms      4.993 ms    n/a
192000                        8.330 ms        5.663 ms        4.330 ms      n/a               n/a

From all the available data I calculated my approximate “hidden” system delay for each sample rate:
44.1 kHz – 4ms; 48 kHz – 3.75ms; 96 kHz – 3ms; 192 kHz – 2.7ms.

So it is not that big, but it does matter as it can have a difference between feeling the delay and not feeling it.

I am using sample rate of 48 kHz with a buffer size of 64 samples, when I am recording or just playing a guitar, and that gives me total delay of about 7.7 ms, which is equivalent to the distance of about 2.64 m. And that works very well for me.

If my laptop could handle higher data rates I would be recording everything at sample rate of 96 kHz just to have an extra resolution when I need it, for example, for sound design, when audio is being stretched.

So, to take advantage of the virtual instruments and software amp simulators, get a computer with a fast CPU and a good audio interface with solid drivers, set it up so the round trip latency does not exceed about 10 ms and you’ll be fine.

RME makes their own everything, which is why their stuff is top-notch. Universal Audio [5] makes Apollo interfaces with DSP units on-board and they have some guitar amp simulations that can run on these interfaces. Basically you can run their entire plugin collection with near zero latency while tracking, which is truly amazing. I would like to get my hands on one of the Apollo interfaces and see what it can do, but I can wait until they start supporting Thunderbolt and AAX on PC. MOTU [6] is the only company at the moment that has an interface with Thunderbolt support for PC. And, of course, you can always use dedicated units like Line 6 PODs, Fractal Axe-FX etc. that were specifically designed for this purpose and have near zero latency.

 

References

[1] The Truth About Digital Audio Latency. Retrieved 23 April, 2014, from https://www.presonus.com/community/Learn/The-Truth-About-Digital-Audio-Latency

[2]Round Trip Latency. Retrieved 23 April, 2014, from http://www.soundonsound.com/sos/apr12/articles/pc-notes-0412.htm

[3] Audio Interface – Low Latency Performance. Retrieved 23 April, 2014, from http://www.dawbench.com/audio-int-lowlatency.htm

[4] RTL Utility. Retrieved 23 April, 2014, from http://www.oblique-audio.com/free/rtlutility

[5] Universal Audio. Retrieved 23 April, 2014, from http://www.uaudio.com/

[6] Motu 828x. Retrieved 23 April, 2014, from http://www.motu.com/products/motuaudio/828x


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