What is Frequency Distortion

Content Summary

This article provides a detailed introduction to Frequency Distortion, explaining its causes in accordance with the national standard GB/T 2900.86-2009, and analyzing its specific manifestations in dynamic microphones, condenser microphones, and wireless microphones. By integrating content from “Fundamental Frequency Analysis,” “Frequency Response Analysis,” and “Harmonic Distortion Analysis,” it explains the impact of frequency Distortion on audio quality and how to reduce distortion through technical means to enhance the overall performance of audio systems.

Frequency Distortion: Frequency Response Challenges in Audio Systems

In the field of audio engineering, frequency distortion refers to the change in the amplitude of the output signal as the frequency varies when multiple signals with the same amplitude but different frequencies are input. This phenomenon causes changes in the spectral characteristics of the audio signal, thereby affecting the quality and accuracy of the sound.

According to the national standard GB/T 2900.86-2009:  

“Frequency distortion is caused by the linear reactance components of a circuit, characterized by the generation of new frequency components in the output signal that are not present in the input signal.”  

This article will analyze the causes of frequency distortion from an electroacoustic perspective, examine its effects on different types of microphones, and explore technical methods to reduce frequency distortion and enhance the overall performance of audio systems.

A. What is frequency distortion?  

1. Definition of frequency distortion  

Frequency distortion refers to: when multiple signals with the same amplitude but different frequencies are input, the amplitude of the output signal changes with frequency. This is typically caused by different gain levels applied to signals of different frequencies by audio equipment such as amplifiers or filters.  

For example:  

When a sound signal containing multiple frequency components is input;  

If certain frequencies are over-amplified or attenuated;

the output sound may sound “unbalanced” or “distorted”;

2. The Relationship Between Frequency Distortion and Frequency Response  

Frequency response describes how an audio system amplifies or attenuates signals of different frequencies. An ideal frequency response should be flat, meaning all frequency signals are uniformly amplified or attenuated. However, in practical applications, due to device limitations, the frequency response is often not completely flat, which can lead to frequency distortion.

B. Main Types of Frequency Distortion

1. Amplitude Distortion

Amplitude distortion refers to changes in the amplitude of signals of different frequencies after passing through an audio system. If certain frequencies are overly amplified or attenuated, it will result in amplitude distortion.

2. Phase Distortion

Phase distortion refers to changes in the phase relationship of signals of different frequencies after passing through an audio system. Such phase changes can affect the spatial sense and clarity of sound.  

3. Combined Distortion

Combined distortion refers to situations where both amplitude distortion and phase distortion are present simultaneously. This is a common phenomenon in most actual audio systems.  

C. Analysis of the Causes of Frequency Distortion  

1. Uneven Frequency Response of Amplifiers

Amplifiers provide different gains for signals of different frequencies, leading to over-amplification or attenuation of certain frequencies. This is typically due to the varying impedance characteristics of internal components such as capacitors and inductors toward different frequency signals.  

For example:  

At high frequencies, capacitors have lower impedance, which may cause high-frequency signals to be over-amplified;  

At low frequencies, inductors have higher impedance, which may cause low-frequency signals to be attenuated;

2. Improper filter design

Many audio devices use filters to optimize frequency response, but improper design may introduce frequency distortion. For example:

High-pass filters are used to suppress low-frequency noise, but improper settings may cause low-frequency signals to be overly attenuated;

Low-pass filters are used to prevent high-frequency distortion, but improper settings may cause high-frequency signals to be overly attenuated;

3. Compression encoding during wireless transmission

Some wireless microphone systems use digital compression algorithms to transmit audio, which may result in the loss or incorrect reconstruction of certain frequency components, thereby introducing frequency distortion.

D. Frequency distortion in different types of microphones

Different types of microphones exhibit varying degrees of frequency distortion due to their structural differences and operating principles.

1. Dynamic Microphones  

Dynamic microphones are known for their durability, but they are prone to frequency distortion in high-sound-pressure environments.  

a) Amplitude distortion caused by limited high-frequency response  

The diaphragm and coil structure of dynamic microphones have weaker high-frequency response, leading to attenuation of high-frequency components.

For example:  

The Shure SM58 has a high-frequency response cutoff at 15 kHz;  

For vocals or string instruments with rich overtones, this may result in insufficient high-frequency components;  

b) Frequency distortion introduced by filters  

Some dynamic microphones have built-in low-cut switches to suppress low-frequency noise, but this may also cause low-frequency amplitude distortion, affecting the “tightness” of the sound.

2. Condenser Microphones

Condenser microphones, with their high sensitivity and wide frequency response, are commonly used in professional recording but rely more heavily on filters and preamplifiers, making them more susceptible to frequency distortion.

a) Amplitude distortion introduced by internal filters

High-end condenser microphones often incorporate high-pass filters, low-cut switches, etc., to optimize recording environments. However, while these filters suppress noise, they may also cause low-frequency amplitude distortion, affecting the “tightness” of the sound.  

b) The impact of preamplifier design on frequency response  

The preamplifier is a critical component of condenser microphones, and its design directly affects the linearity of the frequency response. If the preamplifier uses a non-linear circuit design, it may introduce frequency-dependent amplitude distortion, affecting the clarity of the sound.

3. Wireless Microphones

Wireless microphones are more prone to multi-band amplitude distortion during signal transmission due to factors such as encoding, modulation, and transmission delay.

a) Amplitude Changes Caused by Multipath Interference

In complex environments, wireless signals may reach the receiver via multiple paths, causing signal叠加 or cancellation, resulting in “blurred” or “unstable” sound.

b) Amplitude distortion caused by digital compression algorithms  

Some wireless systems use compressed encoding to transmit audio, which may result in certain frequency components being overly attenuated or lost, affecting sound balance.  

E. How to measure and control frequency distortion?  

1. Measurement methods  

Use an audio analyzer (e.g., APx500, SoundCheck);

Input multiple sine waves at different frequencies;  

Analyze the frequency response curve of the output signal;  

Evaluate amplitude changes at different frequencies;  

2. Control strategies  

a) Select high-quality audio equipment  

Choose microphones and amplifiers with flat frequency response to reduce the likelihood of frequency distortion.  

b) Optimize filter design  

Design filters appropriately to ensure they do not introduce excessive amplitude or phase distortion.

c) Control wireless transmission paths  

Use radar frequency scanning to avoid interference bands;  

Ensure there are no obstacles between the transmitter and receiver;  

Reduce multipath interference;  

F. Frequency distortion is a critical quality factor in audio systems  

Whether it's dynamic microphones, condenser microphones, or wireless microphones, frequency distortion (frequency distortion) is a key factor affecting sound quality.

From the stability of the fundamental frequency to the integrity of the frequency response, and the accuracy of the sound power level, every stage can be a source of frequency distortion. Only through scientific selection, proper use, and good maintenance can frequency distortion be minimized to restore true, clear, and natural sound.

As a professional Microphone Manufacturer, we have fully considered frequency response optimization mechanisms in the product design stage to ensure that every product delivers exceptional audio performance in various usage scenarios.