What does phase mean in speakers, musical instruments, and audio?

My understanding is that phase has two meanings. Let’s use a two-way two-channel speaker as an example. For example, if the left and right channels are out of phase, the sound will not be able to form a three-dimensional audio image. If the high frequency and low frequency are out of phase, the high and low frequencies cannot be conveyed to the listener's ears at the same time, and the sound will be unnaturally separated. picture. I don't know if the answer is correct or not.

What does the phase of a sound system mean? How to position it for the best sound quality?

Physics Rules

At its most basic, phase refers to sound waves — simply the vibrations of air. When we hear sound, air pressure changes what we hear. Just like the ripples caused by a stone falling into water, the sound is created by the movement of air. As in water, these movements cause a ripple effect. Waves consist of crests and troughs. These cause our eardrums to vibrate, and our brains convert these thoughts into sounds.

When we record sound, the microphone's diaphragm essentially replicates the behavior of our eardrums, vibrating with these waves. These peaks cause the microphone's diaphragm to move in one direction, while their troughs move in the opposite direction.

Just phase

When using multiple channels to record with a sound source (such as stereo miking of a guitar, multi-mic miking of a drum kit, or using a microphone to mic a bass) pickup), phase problems will occur. Using "Mono Overdub" avoids this problem, but doesn't give you a dynamic stereo soundstage. In fact, this problem is often revealed during the conversion from stereo to mono.

Figure 2 shows the two channels of the signal. When both channels are in phase, our ears hear equal amplitude at the same time.

But if one side of the stereo signal is inverted, as shown in Figure 3, the signals go back to canceling each other out. In fact, if we take a pure sine wave and combine two signals that are out of phase, the result will be silence because the sounds cancel each other out.

Of course, in the real world, we usually cannot hear pure sine waves. Because most of the music we hear, and most of the instruments we record, is made up of multiple waveforms and harmonics, the results of phase cancellation can also be quite complex.

For the listener

For the average listener, phase cancellation occurs when wiring your audio equipment incorrectly or accidentally flipping the polarity of a channel. Don't be surprised, many Giti stereo systems and even project studios have their monitors wired out of phase. In some circumstances, if you don't listen carefully, you won't be able to discover anything. This is often called "out-of-phase wiring" and is technically a matter of polarity. In other words, the effect heard by polarity reversal is the same as phase cancellation.

The easiest way to check your sound is to convert your mix to mono. Many stereo systems and most mix controllers allow you to do this with a simple one-touch operation, however, some signs of phase issues can also be found in stereo.

What do phase problems sound like? Because phase cancellation is obvious in the low frequency part. Therefore, the result of out-of-phase monitoring is that the sound is thin, with no or only a small amount of low-frequency sound. Another possible result is a lack of positioning on the kick drum or bass guitar. For example, the kick drum might move around in the mix rather than coming from the same point.

Another stereo out-of-phase phenomenon is that the signal placed in the center disappears, while the sounds placed at the extreme positions are retained. Usually the main part of the main voice or solo instrument disappears.

In the recording studio

Phase issues can become complicated in recordings where there are no different levels. In most recording projects we deal with multiple instruments and microphones. Because waves of different frequencies will reach different microphones at different times. Therefore, it is very possible that the diaphragm of one microphone receives a positive phase, while the diaphragm of another microphone receives an opposite phase. The phase relationship between these different waveforms will be difficult to predict.

In fact, the more microphones are used, the harder it is to avoid phase problems.

Let's examine a simple scenario, such as a stereo recording of an acoustic guitar. Usually, the configuration of the two microphones is that one cardboard box hole picks up low frequencies, and the other cardboard box fingerboard picks up transient details. Of course, the frequency range of a guitar covers several octaves, which means that it includes sounds of various wavelengths. Because the microphone is at a fixed distance from the sound source, those different waveforms will reach the microphone at different times. Inevitably, there are some harmonics that will sound weak. You're better off moving the mic slightly, as moving the microphone less than an inch can make a big difference. Until your ears can no longer hear the sound. Another solution is to treat it as "center, side" pickup technology, which will not be explained in detail here.

Positive phase

So, how to correct the phase problem? Most of the time, it just depends on the situation. Suppose you find a phase problem during the recording process. The easiest way is to move the microphone, or reverse the phase on the microphone or input channel.

When you are trying to capture the atmosphere, there is also a good little trick: microphone swing...

What is phase in speaker theory?

In the sound reinforcement system, due to the reverse polarity of the microphone signal output line or the speaker power signal input line and the phase distortion in the system, various sound anti-phase or phase shift problems will occur. The correctness of the sound phase relationship (especially the reverse phase) will directly affect the quality of sound restoration. However, the current audio industry seems not to attach great importance to the phase reversal and phase shift of the system. After most audio workers connect the system, they do not consider the phase of the microphone and speakers at all; when adjusting equipment and systems, they do not consider a series of phase distortions that may be caused by adjustments, which is very important for modern audio systems. , is undoubtedly a shortcoming. This article discusses various phase issues in the audio system, analyzes the impact of phase shift on reproduced sound, and specific methods for checking and solving phase reversal situations. The phase reversal of the audio system includes two aspects. One is that for audio signals, the phase difference between two identical sound signals is 180°; the other is that for microphones and speakers, driven by the same sound, each speaker vibrates. The vibration directions between membranes, microphone diaphragms, or between speakers and microphone diaphragms are opposite. Inversion and its effect on sound can be clearly understood from practical applications. To sum up, there are 5 types of phase inversion in the sound reinforcement system, namely phase inversion between left and right channel speakers, true phase inversion, microphone inversion, phase inversion of some speakers in an array of multiple speakers, and phase inversion in one speaker. Different speakers are out of phase. Any sound system may have varying degrees of phase shift or phase distortion, which has a certain relationship with the phase-frequency characteristics of the sound equipment itself and the adjustment of the sound system. Left and right channel speaker phase In order to reproduce the stereo effect, make the broadcast sound have a good sense of expansion and ensure a uniform sound field, modern speakers adopt a two-channel system for sound playback. When the left and right channel speakers play sound at the same time, if the same push signal is sent to the left and right channel speakers, the vibration directions of the speaker cones should be exactly the same, that is, they should move outward or inward simultaneously; if the vibration direction of the diaphragm On the contrary, the vibration direction of the sound waves emitted must be opposite, which is equivalent to a 180° phase difference between the sound waves emitted by the left and right speakers. This state is called the left and right channel speakers being out of phase. The inversion of the left and right channel speakers will have two effects: (1) The sound emitted by the left and right speakers will vibrate in exactly the opposite direction in the sound field. The sound energy of each other will offset each other in the sound field, causing an acoustic short circuit phenomenon, resulting in The volume of the playback sound is not as high as it should be, the sound intensity becomes poor, the bass is muddy, etc. (2) Since there is a 180° phase difference between the left and right channel sounds, the sound image positioning when playing back stereo music depends to a large extent on the phase difference between the left and right channels.

Stereo theory tells people that when there is a 180° phase difference between the left and right channels, the listener will feel that the stereo sound image has moved to the outside of the two speakers, and the position of the sound source is erratic, blurry and chaotic. The unique presence of stereo sound The effect of sound, space and sound envelopment is destroyed. It is very easy for the sound system to reverse phase during installation and connection. To prevent this phenomenon, the signal input terminals of some speakers and the output terminals of the power amplifier are marked with red and black colors to indicate the polarity. Generally speaking, you only need to use a speaker cable to connect the red end of the power amplifier to the red end of the morning speaker, and the black end of the power amplifier to the black end of the speaker. But this is not always the case, because it is not ruled out that the signal wires are incorrectly connected during the production process of the speakers. The polarity of the terminals of some speakers has been reversed when they leave the factory. There is another reason that may lead to an increase in the reverse phase of the speakers. That is to say, modern professional speakers and power amplifiers have generally used Neutrik plugs as audio power signal transmission interfaces. It is not easy to determine the polarity of this interface when connecting. If you are not careful, the polarity of the wires may be reversed. If there is indeed a reverse-phase situation, just swap the two speaker wires of the reverse-phase speakers. Using the listening method to check whether the speakers are in phase reversal is a simple and easy method. This method can be used when there is no special phase measurement equipment (such as a phase meter). At present, there are special CD audition disks on the market, which record two kinds of sounds, the left and right channels, in phase and reverse phase. Before playing a sound, the listener will be told in advance whether the sound to be played is in phase or in phase with the left and right channels. If the in-phase sound is better than the out-of-phase sound, it means that the left and right channel speakers are in phase; otherwise, it means that the speakers are connected reversely. When there is no dedicated sound test disk, you can use a better quality music program source to check whether there is phase reversal in the left and right channel speakers through sound comparison. When listening, carefully observe the three-dimensionality, strength, and dynamics of the sound between the two connection methods...

I leave the audio phase problem to everyone, thank you

First of all, the phase is not the left and right sound Tao. There is indeed something called sound image (not phase) in audio adjustment, which represents the direction or spatial position of the sound source. "Phase" in acoustics is the attribute of a wave. It describes the vibration position of the midpoint of the wave. For example , the left and right channels, the phase difference between the output sound waves of these two channels should be 180 degrees, which will form a stereo sound. Based on the problem you mentioned, the mixing of accompaniment and vocals is indeed not a simple matter of combining two tracks into one. It’s done. The processing of vocals needs to be adjusted: EQ, dynamic range, mono to stereo, and reverb. I don’t know how to do it as a professional sound engineer. Just the above four points, if done well, it can be very good. The effect.

Please adopt it

What do the waveform, spectrum, acoustic spectrum and phase spectrum in Adobe Audition software mean respectively? 10 points

This is a waveform. The waveform will change accordingly if the sound is high or low

This is a spectrum, which refers to the frequency of an audio frequency. There is nothing above 8KHz on the right, like this Look, this one obviously lacks high frequencies

This is also a spectrum, and the curve in the middle is the frequency of a sound. This is not as intuitive as the one above... There are many instruments for looking at spectrums...

As shown in the picture, the bottom is the sound phase spectrum, also called the phase spectrum... For example, in the picture below

When the sound phase (left and right channels) changes, the curve position will also change. Changes... If it is stereo, it will change in the middle part

The above... I don’t know if it will be helpful to you...

What should the phase of the car audio be? Distinguish whether it is right or wrong?

Use your ears to listen to the CD player, adjust the left and right, and then listen to the bass of the two speakers. If they are right, the bass will be heavier. If they are wrong, there will be no bass. Also pay attention to the position and phase of the sound. If it is, the sound will be concentrated in the middle, if not, the sound will be dispersed

Is it correct to adjust the audio phase in this way?

The phase can only be detected with a phase meter and a special test disk. of.

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How to test the input to output phase of the audio analyzer

One is to input a sinusoidal signal to the device under test , and then analyze the frequency components of the device's response signal to obtain the harmonic distortion. Another simpler measurement method is to first use a band-stop filter to filter out the fundamental frequency component of the response signal, then directly measure the voltage of the remaining signal, and compare it with the original response signal to obtain the harmonic distortion. Obviously, the harmonic distortion obtained by the second method is THD N. Since the total voltage value of the signal is used instead of the fundamental frequency component voltage value, the harmonic distortion obtained is smaller than the actual value, and the actual harmonic distortion is larger. , the greater the error.

Audio analyzer:

Generally speaking, a relatively complete audio analysis instrument should be able to measure signal AC and DC voltage, signal frequency, harmonic distortion, signal-to-noise ratio, etc. parameter. The powerful audio analysis instrument provides spectrum analysis, 1/3 octave band analysis, octave band analysis, sound pressure level measurement and other functions. If you want to build an audio analysis system, you also need a standard audio signal generator as the excitation signal source.

How does the audio phase difference change?

If it is inverted and the waveforms cancel each other out, then use the audit software to select either of the left and right channels and then select the "Insert" function. Change

If the left and right channel phase shift is serious and it is very serious, it may be better to use audit to change the format

This is my personal summary, I hope it can help you

Is this correct way to adjust the audio phase?

The phase can only be detected using a phase meter and a special test disk.

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