Audio Testing Techniques for Noisy Backgrounds
Even the best performances can lose their impact if the recording is full of background hiss, hum, or unwanted sounds. Noise reduction is the process of minimising or removing unwanted sounds from an audio recording. Noise reduction is the process of identifying and removing these unwanted sounds so that the main performance, whether it is a vocal, instrumental, or spoken word, stands out clearly. Noise reduction is important because clean audio is easier to mix, more pleasant to listen to, and sounds more professional. In music production, noise can mask subtle details like reverb tails or quiet harmonies.
While tools like EQ filters, noise gates, and spectral editing can work wonders, they are most effective when combined with good recording habits. Noise reduction is a valuable skill for any beginner in music production or audio recording. Whether you’re an up-and-coming music producer laying down instruments, a sound engineer experimenting with mic placement, or a vocalist chasing that perfect, rich take; getting clean, professional-quality recordings makes all the difference.
One of the possibilities for performing diagnostics of electric machines is by analysing sound emitted by object of interests. Since any interruption in the manufacturing process can cause a serious financial loss for the company, it is very important to prevent unplanned shutdowns of electric machinery. Hence, monitoring and diagnosing the health of electric motors is crucial, and continues receiving more and more attention. The quality of acoustic monitoring is very much dependent on the background noise of the environment in which the machine is operated.
Preventing Noise at the Source
The easiest way to deal with noise is to stop it from entering your recording in the first place. Select a microphone suited to your recording environment. For untreated rooms, a dynamic microphone can pick up less background noise than a condenser. The closer the microphone is to the source, the stronger the desired signal will be compared to background noise. If your input gain is set too high, it will capture unnecessary noise along with the performance.
Turn off noisy devices like fans, air conditioners, or unused electronics during recording. Record at times when external noise (like traffic or construction) is minimal. Even with careful preparation, some noise will almost always make its way into your recordings.
Noise Reduction Techniques
Even with careful preparation, some noise will almost always make its way into your recordings. Equalisation can help remove specific frequency ranges where noise is most prominent. For example, a high-pass filter can remove low-frequency hum, while a low-pass filter can cut high-frequency hiss. A noise gate reduces or completely cuts sound when the audio level drops below a certain threshold. Manually silencing or trimming unwanted noise between phrases or notes is a simple but effective method. Spectral editing tools allow you to see and remove unwanted noise visually.
Tips for Applying Noise Reduction
When applying these techniques, it is best to make small adjustments rather than aggressive cuts. While it can be tempting to remove every trace of noise from a recording, going too far can make audio sound unnatural or lifeless. Aggressive noise reduction can introduce unwanted artefacts such as metallic or “underwater” sounds. Noise reduction should never strip away the richness or character of the performance. Instead of applying heavy noise reduction in one pass, consider using smaller amounts of processing in several stages. Once you think the noise is under control, test your track on headphones, monitors, and small speakers. Balancing cleanliness with natural tone is a skill that improves with practice.
Choosing the Right Tools
Noise reduction is easier and more effective when you use the right tools. Most DAWs come with noise reduction and EQ options that can handle light to moderate noise issues. Specialist tools are designed to remove noise without affecting the quality of the main signal. Select your tool based on your needs, budget, and experience level. For occasional cleanups, built-in DAW features may be enough.
Noise reduction tools can do a lot, but they cannot fix every problem. If the noise is louder than the main signal or spread across a wide frequency range, removing it will likely affect the clarity and tone of your performance. Excessive editing can be time-consuming and may still leave artefacts in the audio. When you re-record, you can take steps to address the original cause of the noise. Even advanced tools cannot always recover heavily distorted or noisy recordings.
Acoustic Analysis in Industrial Environments
Recently, acoustic analysis has attracted more and more attention, and has been applied in many fields - speech recognition, for example. The easy availability today of data collectors and sensors as accelerometers or current probes drives the use of many condition-monitoring systems based on those measurements.
For many years, diagnostics in the industry were performed “by ear,” with subsequent assessment of the emitted sound. Today’s trends in the job market lead to a situation where there is less and less people who are experienced enough to judge the condition of an object by listening to the sound it makes. It is the result of the fact that many people prefer to do office work rather than working in an industrial environment. A solution of the described problems might lie in the usage of acoustic analysis for objects-of-interest diagnostics. Thus far, it has been relatively difficult to create a reliable, acoustic-based condition monitoring system due to the fact that sound measurements are always affected by background noise. However, recent technologies like acoustic cameras are able to successfully localize specific sound components and thus remove the influence of such noise.
A variety of faults that can occur in induction machines have been extensively studied and many monitoring methods have been proposed to detect problems. Most of those methods for condition monitoring of electric motors utilized vibration or motor current signature analysis (MCSA).
The idea of the acoustic camera is to do sound source identification and quantification, and to create a picture of the acoustic environment through the processing of the multidimensional acoustic signals received via microphone array and to overlay that acoustic picture on the video picture. Other possible acoustic camera applications include use as test equipment for non-destructive measurements for sound identification in vehicle interiors and exteriors; trains and airplanes; and for measurement in wind tunnels, etc. Additionally, some studies show the application of acoustic camera for unmanned underwater vehicles, robots and robotized platforms, etc. It can also be used for passive acoustical sensing in battlefield environments.
Acoustic holography technique was used for analysis of the sound source. Acoustic holography technique is a method that is used to estimate the sound field near a source by measuring acoustic parameters away from the source via microphone array. This is a well-known technique. Vibration measurements are one of the most popular methods for condition monitoring of electric motors. Typically, piezoelectric accelerometers are used for measurements of the vibration. For the purpose of the present work, vibration measurements were taken as a reference for the sound measurements. Vibrations were collected with ABB’s MACHsense-P condition monitoring tool.
All vibration and acoustic measurements where done in an industrial environment. Since induction motors are the most widely used machines in industry, two of the same type three-phase induction motors were chosen. Both motors were located relatively close to each other, and both of them were driving centrifugal pumps of the same type through direct coupling. Both motors where operating at the same load level. Motor case 1 is considered healthy while motor case 2 is considered to have a combination of static eccentricity and soft foot. For both of the motor cases, vibration sensors were located horizon- tally on the center of the body of the motors.
For industrial applications, when performing measurements using a microphone, background noise can- not be avoided. The background noise can be filtered out by post-processing methods of the measured signals. This is possible due to the different nature of the measured sound. The background noise (including the aerodynamic noise of the cooling device) is usually a broadband signal with a more or less constant spectrum. On the contrary, the induction machine generates sound that is characterized by many pure tones - at least for the sound produced by electromagnetic origin.