3 Band Equalizer-Line Level

The RDL ST-EQ3 is a compact three-band, line-level audio equalizer for tailoring audio bandwidth with low noise and low distortion. Its LOW, MID, and HIGH bands have center frequencies of 80 Hz, 1 kHz, and 30 kHz, respectively. The available equalization supports three stated goals: creating custom-tailored audio bandwidth, passing voice-band audio, and producing a smile-curve for music. The unit accepts a 100 kΩ balanced or unbalanced bridging line-level input and provides a +4 dBu nominal, 150 Ω balanced output.

Ideal Use Cases

The ST-EQ3 fits line-level audio paths that require defined three-band equalization. For speech-oriented applications, it can be adjusted to pass voice-band audio. Music applications can use the equalizer to produce a smile-curve. It can also be configured around a custom bandwidth requirement using its LOW, MID, and HIGH bands. Balanced and unbalanced bridging input compatibility allows the equalizer to work with either supported line-level signal format, while its output remains balanced at the specified +4 dBu nominal level.

Why Choose This Model

This model combines three-band response shaping with published noise, distortion, frequency-response, and common-mode rejection specifications. The 100 kΩ input supports balanced or unbalanced bridging operation, and the 150 Ω balanced output is rated at +4 dBu nominal. Gain is adjustable from OFF to unity with positive or negative equalization adjustment. The specifications also identify performance under both 600 Ω and bridging output-load conditions, providing clear operating references for system planning.

Installation and Integration

The ST-EQ3 measures 0.7 inches high by 3 inches wide by 1.6 inches deep, equivalent to 1.7 by 7.6 by 3.9 centimeters. Its specified ambient operating environment is 0°C to 55°C. Power must be ground-referenced 24 Vdc at 25 mA. The recommended PS-24AS power supply for the USA or PS-24AX for international use is not included. Integration requires a line-level source connected to the 100 kΩ balanced or unbalanced bridging input and a destination compatible with the +4 dBu nominal, 150 Ω balanced output. Gain can be adjusted between OFF and unity along with the required equalization setting.

Performance Highlights

Each equalization band has a published center frequency and bandwidth at 3 dB EQ:

• The LOW band is centered at 80 Hz and covers 20 Hz to 300 Hz.
• The MID band is centered at 1 kHz and covers 200 Hz to 7 kHz.
• The HIGH band is centered at 30 kHz and covers 3 kHz to 30 kHz.

With the equalizer set flat, frequency response is 20 Hz to 22 kHz within ±0.5 dB into 600 Ω. Into a bridging load, the flat response extends from 10 Hz to 22 kHz within ±0.5 dB. THD+N is specified below 0.030%, with 0.010% typical performance at 1 kHz with a flat response. Noise is below -80 dB relative to +4 dBu, while CMRR is greater than 60 dB from 50 Hz to 120 Hz.

What Makes It Different

The ST-EQ3 is defined by the combination of adjustable three-band equalization and documented operating ranges for every band. Rather than describing only general bass, middle, and treble shaping, its specifications identify the center frequency and 3 dB EQ bandwidth of the LOW, MID, and HIGH sections. The unit also provides two specific adjustment targets—voice-band audio and a music smile-curve—alongside custom bandwidth tailoring. Load-dependent frequency response, CMRR, noise, and THD+N figures further define its performance.

Final Assessment

For a line-level signal path requiring three-band audio equalization, the RDL ST-EQ3 offers clearly specified frequency ranges, flexible balanced or unbalanced bridging input, and a balanced +4 dBu nominal output. Its adjustable gain, low published noise, and low typical distortion support controlled audio shaping for voice, music, or custom bandwidth requirements. Installation planning should include a separate compatible 24 Vdc power supply and operation within the specified 0°C to 55°C environment.