Smaart RTA's SPL Accuracy

Smaart RTA's SPL Accuracy

Using Apple's built-in hardware, Smaart RTA provides accurate frequency response measurements, and representative SPL measurements (hardware dependent). The frequency response measurements (RTA and Spectrograph) are the exact same spectrum measurement engines developed over 20 years and found in the desktop versions of Smaart software (v9+).

The accuracy of the SPL measurements can vary depending on the hardware being used. In this article, we will discuss the accuracy of Smaart RTA's SPL functionality specifically when using Apple's built-in MEMS microphones and how the performance may be impacted over time or in high SPL environments.

Where We Are Now

Smaart RTA's default SPL calibration is based on an average of tested devices and is reasonably accurate at lower levels, before Apple's built-in limiting takes over to skew the displayed values lower than a non-limiting hardware configuration. Generally, this starts to show up at levels above 103-106 dBA SPL. Operating systems supported by Smaart RTA will detect an overloaded microphone and send that information to us, where we will display OVERLOAD in the SPL metric rather than an inaccurate SPL value.

SPL Accuracy with Built-in Microphones

While the app's SPL functionality is fully operational when using Apple's built-in microphones (such as those found on iPhones and iPads), and is extremely consistent from device-to-device, it is important to note that accuracy can be significantly improved by using external hardware. That said, the SPL values that Smaart RTA generates are generally consistent from device to device and day to day. This allows for the information displayed to be a reasonable reference point to compare how loud something is from one day to the next, or show to show.

To achieve more accurate SPL measurements and avoid overload we strongly recommend using external hardware, such as a USB audio interface with a calibrated measurement microphone. These devices are specifically designed to handle higher SPLs and offer a more reliable and precise measurement experience. Calibration is not offered in the base version of Smaart RTA; a Subscription or Lifetime license of Smaart RTA Pro is required to access this functionality.

Frequency Response Accuracy

One of the strengths of Apple's built-in MEMS microphones is their generally reliable frequency response, which makes them useful for many acoustical measurements. While Smaart RTA can bypass the device's high-pass filter, the built-in limiting circuitry remains a constraint. Nonetheless, frequency response measurements can still be trusted when using the internal microphone, provided that SPL levels remain below the overload threshold.

Impact of Microphone Condition

It is important to consider that built-in microphones can degrade in accuracy over time due to factors such as physical damage or the accumulation of dirt/dust/lint. Debris or contaminants can alter the sensitivity and frequency response, leading to skewed results.

Smaart RTA vs Smaart RTA Pro

While the base app provides reasonable accuracy with Apple's built-in MEMS microphones, using external hardware with Smaart RTA Pro is recommended for high SPL environments or when maximum accuracy is required.

The frequency response of built-in microphones remains reliable, but users should be aware of the limitations imposed by limiting circuitry and the potential impact of microphone condition over time. For professional measurements, we strongly advise using a USB audio interface and a calibrated measurement microphone.

For more information on calibrating Smaart RTA, please refer to this guide on our support portal.