Analog Pink Noise Generator for Audio Testing
Pink noise is an essential tool in audio testing, widely used for analyzing speaker systems, room acoustics, and crossover networks. Unlike white noise, which has equal energy across all frequencies, pink noise features equal energy per octave, making it ideal for audio response testing. This characteristic ensures that pink noise offers a flat frequency response when analyzed on a logarithmic scale, providing a more accurate representation of audio systems.
This article describes a pink noise generator designed to meet various audio testing requirements. This device combines simplicity and performance, featuring a minimal component count for ease of assembly without compromising accuracy and usability.
Difference between white and pink noise spectra
Pink Noise in Audio Testing
How does a pink noise source help evaluate the performance of a speaker? Any deviation from a flat frequency response results in a coloration of the noise. With some experience pink noise can be helpful.
Pink noise and also white noise are useful for evaluating speakers regarding difference sound. With a good pink noise source the user can adjust equalization and speaker crossover points and balance systems. Pink noise is also useful for sound masking systems and to provide greater privacy. The spectrum of pink noise approximates that of much music which makes it an excellent test signal for sound systems. Many people select pink noise in place of white noise since higher levels of white noise can burn out tweeters.
Moderate volumes are recommended when testing. Then adjust or EQ different bands of the noise to compare to non-EQ'd pink noise. Just to see what you think you can play pink noise over what you have. Get some feel for how peaks or dips sound. Peaks are easier to hear.
It is, but pink noise has a spectrum closer to music on average and it has a defined slope.
Pink Noise Generator Design
This pink noise generator design uses a reverse-biased emitter-base junction of a 2SC945 transistor as the noise source. In this configuration, the transistor behaves like a noisy zener diode, producing a broad spectrum of white noise.
Components Required
The following components are needed to build the pink noise generator:
- C101, C103 - 100μF/25V
- C102, C104 - 1000μF/25V
- C105, C106, C114 - 10μF/25V
- C107, C115, C116 - 0.1μF/50V
- C108 - 0.033μF/50V
- C109 - 0.01μF/50V
- C110 - 0.0033μF/50V
- C111 - 0.001μF/50V
- C112 - 330PF/50V
- C113 - 100PF/50V
- D101, D102 - 1N4007
- J101 - 5.5mm DC Jack Socket
- J102 - RCA Jack Socket
- Q101 - TIP31
- Q102 - TIP32
- Q103 - 2SC945
- R101, R102, R104, R105, R106 - 1KΩ (5% 1W)
- R103, R107 - 2.2Ω (5% 1W)
- R108, R109, R115 - 100KΩ
- R110, R111, R117 - 10KΩ
- R112 - 1.8MΩ
- R113 - 1MΩ
- R114 - 330KΩ
- R116 - 33KΩ
- R118 - 3.3KΩ
- TP101 - Test pin (optional)
- U101 - NJM4558
All resistors are 5% 1/4W unless otherwise noted.
Step 1: NJM4558 Operational Amplifier
In this design the NJM4558 op-amp is used to amplify and buffer the generated noise, ensuring high input impedance, stability, and consistent performance. At this stage above generated white noise is converted into pink noise using a 3dB/octave filter, which ensures equal energy distribution per octave over the audio frequency range.
Step 2: Power Supply & Noise Source
The unit operates on a single-rail DC power source, compatible with 12V to 18V inputs. At our testing we found that this kit with 2SC945 from Matsushita electric starts to generate output at 8.4V and above. As we noticed this behavior is changing from vendor to vendor. For example some 2SC945's (It's manufacturer is difficult to identify) produces output at 9.1V. By considering most of the datasheets we decided 12V as the safest voltage which guaranteed the output.
Step 3: Combine Noise Generator With LM386 Amplifier
To evaluate the performance of the pink noise generator, we paired it with the Simtelic KT0001 (LM386 power amplifier) module. This setup ensured that the output noise was sufficiently amplified for practical testing scenarios. This kind of setup is useful to identifying anomalies in speakers and crossover networks, measuring and optimizing room responses for audio clarity, and for microphone calibrations.
When connecting this kit to an amplifier, pre-amplifier, or other analog audio equipment, always use shielded audio cables (UL1185 or equivalent) with the shortest possible length. Long, unshielded cables may introduce hum, oscillations, and distortion in the output.
Step 4: PCB
The PCB for this module was fabricated by PCBWay, who generously sponsored this project. PCBWay offers high-quality PCB manufacturing and assembling services. Also, they offer CNC and 3D printing services. The pink noise generator PCB is available to order from PCBWay. It is designed with through-hole components and can be assembled and tested without the need for specialized electronic assembly tools or instruments.
PCB of the pink noise generator
Applications
The ST-NG1 is the ideal choice where random white or pink noise is needed. It is suitable either as a reference noise source for audio measurements or as a masking noise source in engineered sound or counter-intelligence applications. Amplitude limiting circuitry in the ST-NG1 controls extreme peak excursions while preserving random variations of at least 20 dB. The noise generating circuitry in the ST-NG1 is truly random analog noise occupying the full bandwidth from 20 Hz to 20 kHz. This makes the ST-NG1 ideal in masking environments where secure, random noise is required. Unlike the typical digitally generated pseudo-random noise generators which can be decoded and removed by effective intelligence equipment, the ST-NG1 produces no repetitive frequency or amplitude pattern. Wherever white or pink noise signals are needed, the ST-NG1 is the ideal choice.
Here's a summary of typical applications:
- Adjustment of equipment drive levels with constant Hz bandwidth analyzers such as Gold Line RTAs.
- Identifying anomalies in speakers and crossover networks.
- Measuring and optimizing room responses for audio clarity.
- Microphone calibrations.
- Sound masking systems.
Software Tools
REW (free) has a "generator" tool which can create many types test tones including pink and white noise. REW (free) has a "generator" tool which can create many types test tones including pink and white noise. You can play them directly or create a file with it.