Voxengo SPAN is a free real-time FFT spectrum analyzer that became a default insert on mix and master buses long before loudness meters went mainstream. It does not compress or EQ anything. It shows you what is happening in the frequency domain, with enough metering extras to catch level and correlation problems while you work.
It excels at flexible analysis. Modes cover mono, stereo, mid-side, and multi-channel layouts including surround. You can set Fourier block size, window overlap, visual slope, smoothing, and a secondary spectrum (for example real-time or all-time maximum). Output metering adds adjustable ballistics, EBU R128 and K-system scales, true peak clipping detection, headroom estimates, and correlation. That combination is why SPAN still appears in free-plugin roundups years after launch.
The trade-off is purpose. SPAN will not replace a full suite like Insight 2 for detailed loudness workflows or client reports. The UI prioritizes function over fashion. If you only need LUFS targets for streaming, Youlean Loudness Meter may feel more focused. If you need tonal target curves, Tonal Balance Control or REFERENCE aim at different jobs.
Choose SPAN as a free always-on analyzer. Graduate to Insight 2 or Youlean Pro when you need deeper metering features. Download only from the official Voxengo product page.