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Sound System Calibration Tutorial with TRACT

Jun 20, 2018 | 285,072 Views

How can you tune a sound system within just a few minutes? Watch how to calculate a corrective EQ curve and fully time-align any PA system, using the TRACT System Calibration plugin and Rational Acoustics' Smaart audio analysis software.

Since every sound system behaves differently from venue to venue, before mixing, we need to tune the system. Audio professionals around the world rely on accurate audio measurement analysis from Smaart. TRACT receives the data from Smaart, and uses it to make EQ and time-alignment corrections. TRACT, together with Smaart, is a great, fast and accurate way to tune your PA, wedges or studio monitors.

In this video, learn step-by-step how to accomplish three important tasks when tuning a system:

  1. Equalizing a full range PA
  2. Time-aligning front fills to mains
  3. Time-aligning subs to mains

1. Equalizing a full-range PA

To calculate a corrective EQ curve, we’ll need a precise transfer function measurement. To accomplish this, we'll need to route pink noise to Smaart, and then route pink noise through the PA as well.

Capture the noise with a measurement microphone near front-of-house. Smaart will compare the frequency response of the PA to the direct-fed signal. This way, we’ll see how the PA and the environment affect our frequency response – and what needs to be done to offset and correct it.

This is where TRACT comes in: TRACT will calculate an EQ curve to even out the response of the PA, and tune our system.

  1. Insert an instance of TRACT on the matrix output driving the mains
  2. Connect to Smaart
  3. Select the configured transfer input, and set views to “Magnitude”
  4. Play pink noise, and capture traces in a few locations around front of house
  5. Merge the captures into one average, and label it
  6. In the Captures menu, select the merged trace, as well as a desired reference curve
  7. Click the FIR button to create a corrective FIR compensation curve
  8. If you’d like, you can limit the amplitude and frequency ranges of the FIR correction, bring the whole curve’s amplitude up or down, or further supplement it with 8 bands of IIR EQ filters

2. Time-aligning front fills to mains

In larger venues, the main PA doesn’t cover the first few rows too well. To supplement the coverage, small speakers are used as front fills. Since they’re situated so close to the audience, the sound will arrive first to the listeners from the front fills, and then from the mains. This can cause phasing issues, or even a slap delay effect. To avoid these issues, we need to delay the front fills’ signal so that sound from the front fills and the sound from the mains will arrive to the listener at the same exact time: a process known as time-alignment.

To time-align front fills to mains:

  1. Insert TRACT on the matrix output feeding the front fills
  2. Place a measurement microphone close to the front of the stage, where the sound from the front fills and the mains collide
  3. Select your configured transfer input from Smaart
  4. Play pink noise through the main PA speakers, and click “Find Delay.” This value equals the amount of time it takes for sound to arrive at the listener’s position from the mains
  5. Click “Add Delay” so that TRACT will remember this value
  6. Now play pink noise through the front fills, and again click “Find Delay”
  7. Once found, we can see the difference: The disparity in time that it takes for sound to arrive from each source
  8. By clicking “Apply Delta,” we can implement the time difference and delay the front fills’ signal, effectively aligning sound coming from the two sources

3. Time-aligning subs to mains

When running a system’s subwoofers on a separate output from the mains, we often need to time-align the two to avoid phase cancellation of low-end information. If not aligned, impact from instruments such as kick drum and bass may be out of phase, and the whole mix will feel lacking in power.

Since audio from the main speakers covers a frequency range of about 100 Hz and above, and the subs cover around 100 Hz and below, the area where the frequencies cross over is susceptible to phase cancellation.

To phase-align subs to tops:

  1. Insert TRACT on the output feeding the subs
  2. Place a measurement mic on a pillow on the floor near the center of where the audience will be
  3. Select your configured transfer measurement pair from Smaart, and set views to Magnitude + Phase
  4. Play pink noise through the top speakers, and click “Find Delay”
  5. Click “Insert Delay” so that TRACT will remember the value, and capture the trace so TRACT will display the phase readout of the top speakers
  6. Mute the pink noise in the tops, and play pink noise through the subs
  7. Click the Sub Zoom toggle to get a closer look at the crossover range, and note the system’s measured crossover frequency
  8. Now, we need to make sure that the subs’ phase trace is aligned with that of the tops, which we can still see from our capture
  9. If you slowly increase the delay of the subs’ output, the purple phase trace will shift to the left
  10. Using this technique, make sure that the subs’ trace is overlaid on the tops’ trace at the system’s crossover point

And now, you're ready to mix!

Learn more about TRACT System Calibration.

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