Traditional Source-Independent Measurement in Smaart
One of the key strengths of Smaart’s transfer function measurement is its source-independent approach. This allows engineers to analyze a system’s response using any ongoing audio signal passing through it—such as live speech or music—without needing a specific test signal.
Benefits:
- Measurements can be taken under real-world operating conditions.
- Engineers can evaluate the system while simultaneously listening to the program material.
- No need to interrupt the signal flow or control the input source, which is often impractical in live settings.
However, using random (non-periodic) signals with the Fast Fourier Transform (FFT) algorithm introduces challenges. The FFT assumes the captured data represents either the complete signal or one full cycle of an infinitely repeating periodic signal.
Random signals don’t naturally meet this requirement, leading to:
- Mathematical noise (artifacts like leakage).
- Instability in the measurement data.
To address this, Smaart applies a data window (e.g., a Hann window) to the signals. This window applies a gentle “fade-in” and “fade-out,” making the data appear more periodic and significantly reducing noise and instability.
Trade-offs of windowing:
- Slightly higher measurement noise floor.
- Minor spectral spreading (broadening of frequency peaks).
These effects are generally minor and do not significantly impact accuracy, especially when sufficient averaging is used.
SyncSource™: Source-Dependent Measurement in Smaart v9
Smaart v9 introduces SyncSource™, a new transfer function mode that eliminates the need for data windowing entirely.
How it works:
- It uses a pseudorandom excitation signal (pink noise or sweep) generated by Smaart’s built-in signal generator.
- The signal’s cycle length is precisely matched to the FFT size, creating a truly periodic signal.
This is known as a source-dependent measurement because it requires Smaart’s signal generator as the input source.
Advantages:
- No data windowing needed, resulting in cleaner data.
- Greater measurement stability.
- Higher coherence values (better correlation between reference and measurement signals).
- Reverberant energy in the room becomes correlated with the reference signal, preventing it from degrading coherence.
SyncSource™ is particularly useful in challenging acoustic environments and is available in Smaart Suite and RT editions (enabled in Advanced Preferences).
Example of Random Source TF Measurement (top) versus SyncSource™ TF Measurement (bottom)
SyncSource™ TF measurements are available in Suite and RT editions of Smaart. To enable synced-source measurements, go to the “Advanced” tab of the Options > Preferences dialog and check the box labeled “SyncSource™ TF” in the Transfer Functions Settings area:
When a SyncSource™ measurement is enabled, a field is added in the transfer function control bar for the user to specify their Stimulus type – either Random or Synchronised. If “Synchronised” is chosen, a second measurement parameter field labeled “Length” is added for the user to set the FFT length that will be used for both FFT size and the Generator source.
Example of Transfer Function Control Bar with SyncSource™ disabled (left) and enabled (right)
Choosing Synchronized as the Stimulus will:
- Limit the Signal Generator choices to only Pseudo-Random noise or Sweep
- Set the FFT size / Period Length of both the transfer function measurement engine(s) and the Generator source to the length specified in the Control Bar Length setting. These controls become inaccessible in Transfer Function measurement settings and Generator Settings
- Limit the available settings for Transfer Function FFT size to 16k and larger
- Disable any Transfer Function engines configured as exempt from Global FFT size setting, and pop an error message stating the same
- Disable the transfer function measurement data window
MTW is still calculated simultaneously, using the pseudorandom noise source and FFT data windows.
SyncSource™ TF provides excellent measurement stability and improved coherence, even in the presence of excessive external noise, without the need to increase the measurement level significantly above the noise floor. However, synchronised measurements do require the use of Smaart’s signal generator to be used.
source: https://support.rationalacoustics.com/support/solutions/articles/150000069513-what-is-the-syncsource-transfer-function-
Smaart is excellent on its own, but most users find they get much more out of it after some structured training. That’s where our seminars come in. At TZ Audio we run practical seminars, both online and in-venue. We offer seminar-only or full “all you need packages” including software & hardware. It’s simply the fastest way to become comfortable and confident with the measuring a sound system.
If you’re in Norway, Sweden, Denmark or Iceland – or elsewhere – we offer is online seminars and traveling to Norway is a valid option too of course. We’re here if you have any questions about the software or upcoming seminars.
Thanks for reading!