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SIA Smaart Live for Beginners

An earnest attempt to explain SIA Smaart Live concepts and implementation in a fashion easily digested by the beginner.

By Doug Fowler May 1, 2008

A Transforming Experience
Smaart picks the incoming audio off the A/D converter on the computer sound card and then compares the two signals. In order to efficiently manipulate the waveforms a Fast Fourier Transform is employed. Mathematically inclined readers may do a web search and find a wealth of information on this subject. Jean Baptiste Fourier was an eighteenth century French mathematician who discovered a method of converting a waveform or function into sine waves of different frequencies which sum to the original waveform. By doing this, it becomes much easier to manipulate the waveform.

The Fast Fourier Transform is able to take advantage of data which is represented in powers of 2, which of course is ideal for digital computing. In everyday use it is not necessary to understand the mathematics behind Smaart but it is presented as an interesting side note for the average user.

Thus, Smaart is an FFT Analyzer which compares a source (reference) signal to a measurement signal. It is very important to note that Smaart, or any other FFT analyzer, does not care what the source signal is as long as it is random enough to be distinguishable in discreet chunks. This means that FFT analyzers can use music as a reference signal if desired. The logical extension of this is Smaart can be used to measure during a performance, whereas other methods of measurement such as TEF rely on a known source signal to perform measurements.

It’s a Dual Channel FFT Analyzer
Recall that Smaart requires two channels in order to compare one audio signal to another. For now, we will work with the output of a console and a measurement microphone. The console output is the reference channel and the measurement microphone output is the measurement channel. Smaart compares the two in order to yield the transfer function, which displays the difference between the two signals.

So, we need to get two channels of audio into the computer. The simplest way to accomplish this is via the line inputs of the sound card. Note very carefully: not all laptops have line inputs, and those that do often have only mono inputs. A stereo line input is required, unless you choose to get audio into the computer via a USB device or other external hardware. For now we will assume a laptop with a stereo line input. Don’t try to use the microphone input, it is mono and has a difficult time with line level signals.

Why can Smaart use that inexpensive sound card chip found in laptops? Smaart takes the audio from the analog to digital converter at the hardware level and does not rely on the chip to do all the work. Interestingly, almost all laptops use the same chip at the hardware level. Because of this Smaart supports virtually all laptop audio line inputs.

By convention, Smaart assumes the left channel of the laptop sound card to be the measurement signal and the right channel the reference signal. We need to get audio into the sound card, so let us examine a simple connection scheme using a small mixer:

Simple Interconnect
A simple interconnect scheme for Smaart would involve taking console output and the measurement microphone to a small mixer, which feeds the computer sound card:

In order to “tap” the console output in this example we need a “Y” cable to split the output. There are some issues with this arrangement. Certainly you would not want your console output to “see” the sound card, electronically. Using the measurement mixer solves this problem. In the event one chooses to take console output directly to the sound card without the benefit of the measurement mixer, it is necessary to use an appropriate transformer. Use a measurement mixer of some sort: this is generally agreed upon as the best solution.

Another method which works for larger consoles is to use a matrix output, with the desired channel (house left or right) assigned to the matrix.

The “laundry list”:
1. Take console output (left or right) into a channel of the measurement mixer as your reference channel
2. Send measurement microphone output into another channel of the measurement mixer as your measurement channel
3. Pan the measurement channel left
4. Pan the reference channel right
5. Ensure all channel EQ is flat or bypassed
6. Send the measurement mixer left output to the left channel of the sound card line input
7. Send the measurement mixer right output to the right channel of the sound card line input

Now we have signal properly routed and present at the computer sound card input. The next step is to use the Windows audio mixer to manipulate the sound card line input.

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zolkifli bin sam says

i need a free basic software for eq thank you

Give A. Shit says

Very good information, but why stop there? I’d love a case study where you actually use this in a real life senario.

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