Basic introduction to the mixer
As a modern musician, you often see a mixer. It's the kind of device that has countless knobs and all kinds of switches, and it looks scary. A guy who claimed to be a sound engineer was hiding behind a mixer, not knowing what he was doing. If he's a master, your performance will be very cool! Maybe you're curious, but don't mind if you don't use a mixer – that's professional equipment! Will not use is the should.
But now more and more friends want to record samples of themselves at home and start playing computer music. So there are always all kinds of mixers. Analog, digital, audio interfaces may also have built-in mixer interfaces, as well as mixers for audio software that seem to be more confusing. In short, you will find the shadow of the mixer everywhere. Many friends think that the mixer is very complicated and can't understand. Engaged in half a day without even a sound, depressed! Or do not understand the principle, the wrong use of the mixer, so that it does not play its due role.
Figure 1: Physical picture of the mixer
To learn something, we should first know what the thing can do! What can we do with a mixer? There can be roughly the following items:
The mixer can amplify the signal of the input channel and adjust the equalization (EQ) of the input sound, and even other effects, such as compression, etc
2. The mixer can mix many sounds to form a stereo sound!
3. The mixer can "return" the listening for musicians and actors.
4. The mixer assists the effects to add reverb, delay, etc. to each channel
5. The mixer sends the sound of each channel to a multi-track recorder or audio interface for track recording
6. The mixer can make it easy for the sound recordist to monitor all channels without disturbing these channels.
Practice is the best way to learn a mixer. We take the behringer UB1622FX analog mixer, which is more common on the market, as an example, to introduce the basic functions and use methods of the mixer. Although this UB1622FX mixer is small, it is relatively full of functions and has a built-in digital effect. First of all, I would like to state that I am not a "childcare" of Behringer, I just want to use a specific example to let you know some of the basics of the mixer! Knowledge is common, as long as you master the basics of the mixer, you can quickly master and use a variety of mixers, whether analog or digital, or even those virtual mixers, can quickly get started.
Below we will introduce the functions and use of the mixer in combination with the actual situation of the Behringer UB1622FX mixer.
Part I: Amplification of signals, parameter equalization and insertion effects
We know that the audio signal generated by the microphone is very weak. The output signals of other devices, such as synthesizers, audio interface outputs, etc., their signals are many times stronger than the microphone signals, and their signal sizes are also different and uneven. We need a device to resize these large and small sound signals to the same size to mix. This kind of equipment is the preamplifier, commonly known as the microphone amplifier. Please take a look.
Preamp section of the UB1622FX
Figure 2
Looking at the picture, the large round socket is called the cannon "Cannon" socket, which is used to connect microphones or some professional equipment that also uses a Cannon socket. The jack under the Cannon socket is the TRS jack, which is generally used to connect the signal of the line level. Idea, these two sockets can not be used at the same time! And because of the design of the line, on this mixer, you can't plug the device at the line level into the "Cannon" outlet!
The preamplifier has a control knob, called "TRIM" on the UB1622, "GAIN" or "sensitivity" on some mixers, Chinese name is fine-tuning, gain, or sensitivity. It is commonly known as "mouth". The "Mouth" knob is used to control the signal to put a large number. As for how much to zoom in to ground, it depends on the "PEAK" peak indicator on the channel. If the "PEAK" light blinks occasionally, it's normal, and if it blinks quickly, your input signal is distorted! You need to make the mouth a little smaller!
The [LOW CUT] bass cut switch filters out low-frequency sounds that are not needed.
Another switch associated with the preamplifier is the Phantom Power switch. If you connect a condenser microphone you must turn on the "phantom power"! Otherwise, no matter how big the "mouth" you open, there will be no sound.
Phantom power switch
Figure 3
The Phantom Power Switch, on the back of the UB1622FX mixer, is capable of applying phantom power to all Cannon outlets.
Having said that most of the front placement, let's look at the parametric equalizer.
There is usually a parametric equalizer on the general mixer channel, and on this Behringer UB1622FX mixer, there is a three-and-a-half-parameter equalizer. As shown in the figure.
Three-stage half-parameter equalizer
Figure 4
The so-called parametric equalizer refers to an equalizer that can control the center frequency, Q value (bandwidth), and increase or decrease the amplitude of the frequency. The three-band of a half-parametric equalizer means that this equalizer can adjust three frequency bands, namely treble midrange and bass. The midrange part can be adjusted for the center frequency and its frequency increase or decrease. Because there is no adjustment of the Q value, it is semiparametric equalization.
The knowledge of balance is too deep! The important criterion for testing the level of a sound recordist is not IQ, but EQ. Let's study the knowledge of balance in depth later.
Only very advanced mixers will have dynamic processing, but this does not prevent the UB1622FX from expanding this capability as well. How do you scale it? The mixer uses a special jack called an insert to do this job.
The UB1622FX's Insert jack is on the back panel of the mixer
Figure 5
The Insert insertion point jack has a very special structure. By default, it is connected inside the mixer. When we insert a large three-pin plug. The internal connection is cut off, and the sound is sent from the head (Tip) of the large three-pin plug to the input of an effect, and the signal processed by the effect is returned from the "Ring" of the large three-pin plug to the mixer. For example, a compressor can be connected to a mixer in this way!
Take a look at the schematic
Figure VI
For the Insert jack, we also have a usage, which is to use it as a Direct OUT socket!
The Direct OUT output is typically taken after the preamplification circuit. Can be sent directly to multi-track audio recorder or audio interface recording. The premium mixer back has both Insert and Direct OUT jacks. The UB1622 mixer does not have a Direct OUT output, but we can use the Insert jack for Direct OUT output. As mentioned above, the sound of the input channel can be sent from the TIP of the large three-pin plug to the input of an external device, but if the device is the input to the audio interface, then no sound is returned to the mixer. This way the sound path inside the mixer will be cut off! This channel is silent! What to do? Very simple! Just connect the tip and RING parts to keep the channels of the mixer connected! This way we can use the Insert jack as a Direct OUT!
Figure VII
The Insert jack is retrofitted for Use with a Direct OUT output. Connect the "tip" and "ring" of the big three-pin plug directly!
In fact, the microphone amplifier and equalization are not the core content of the mixer, because the speech playback, balance, have special equipment, and the mixer has these functions just to be able to facilitate the work. Some very simple mixers have no words to play, and there is no balance, not to mention that the mixer interface in the software has no words to play, but we still call them mixers. So what is the most fundamental job of a mixer?
Part II: Panoscopic, fader, and stereo busbars and groups
If we simplify the mixer step by step, we will eventually discover its most fundamental work - as its English name MIXER, that is, to mix the sounds of the various inputs in proportion to become "stereo"! That's the core job of a mixer! Because even the simplest mixer can do it!
Stereo, two speakers or headphones to listen to music? be! Listening is of course the easiest thing to do! But if you want to create stereo sound with a mixer, it's not so simple! The knowledge here is great! Let's start with how the human ear discerns the direction of sound.
In simple terms, a person can distinguish the direction of a sound because he can distinguish the intensity and time that a sound reaches both ears. For example, there is a mosquito on our left and its buzz can enter our left ear without blocking. And because the head blocks the sound, the sound heard in the right ear is certainly not as big as the left ear. So our brains will judge that mosquitoes come from the left! This is how the human ear determines the direction of sound based on the difference in the intensity of the sound. So what's going on with the time difference? Very simple! The mosquito is on our left side, so it's closest to our left ear, so the left ear hears the sound first and the right ear behind! Our brains can also discern this very subtle difference!!! In this way, humans judge the direction of sound by feeling the difference in intensity and time of sound in both ears! People can also imagine the location of mosquitoes with their eyes closed, just like they can see, which is called sound image, huh!
So how does the mixer control the direction of the sound? For the mixer to create a sense of direction for sound, it needs to have two left and right channels corresponding to our left and right ears. The principle of the human ear using the difference in sound intensity above to determine the direction, when the volume output of the left channel of the mixer is greater than the volume output from the right channel, our ears will believe that the sound is from the left. The mixer adjusts the pan icon knob (PANPOT in English)! When the pan knob is adjusted to the left, the signal will be sent more to the left channel, and the human ear will believe that the sound comes from the left when it hears that the sound intensity of the left channel is greater than that of the right channel. vice versa. When the sound image knob is adjusted to the middle 12 o'clock position, and the volume of the sound sent to the left and right channels is the same, then the human ear will think that the sound comes from the front. This is the basic principle of stereo sound making with audio and video knobs on mixers. Of course, there are other ways to create stereo sound, such as using the delay effect to create a sense of direction, which will not be discussed in this article.
Figure 8: Schematic diagram of controlling the direction of sound with a mixer
The picture above is a schematic of how we use a mixer to control the direction of the sound! Adjust the pan knob to control the sound "direction"
The direction of the sound is fixed, and we also have to control the size of the input sound in each channel. We know that with the volume knob you can control the sound size. On the mixer, engineers put volume knobs usually designed with long strips of putters. Its scientific name is "attenuator", and its common name is "fader".
The advantage of using a pusher to control the volume is that we can more intuitively "see" the size of the volume. As I said, the mixer preamplifier has adjusted the signal of each channel to the same level. If each channel is set to the same standard level value. Then, the position of each fader can also reflect the approximate volume of the channel. We can even know the level of this channel based on the tick number next to the fader, which is really clear at a glance!
With the audio-visual knob and fader, the mixer can control the direction and size of the sound, but this is only a mono case. How are multiple channels of sound mixed? Here must introduce a very important concept of the mixer, that is, the "bus", its English is BUS, bus? Of course not! In this case, it refers to the common channel of the sound signal. The mixer is able to mix the sounds of each channel into a "stereo" because it has a main stereo bus. The stereo bus consists of two single-channel busbars—left channel L and right channel R.
Figure IX
In this figure, the sound is shown going through fader attenuation into the pan control knob, which sends the left and right signals to L and R of the stereo bus, respectively. This way we can mix the sound of multiple input channels into "stereo"! This is a schematic diagram of the work of a most basic mixer. Even the simplest mixer can accomplish this task! It should be said that this is the most basic concept and application of the mixer!
Specific to UB1622FX, we look at the situation of one of his input channels!
Figure 10
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[PAN] sound and image knobs and faders, it should be no problem! Look at a few switches in the figure: the [MUTE] mute switch, the [SOLO] solo (or PFL switch), the [MAIN] main stereo busbar switch, the [SUB] sub-marshalling busbar switch.
The first is the [MUTE] mute switch
[MUTE] mute switch
[MUTE] the power of the switch is great! Because once you close it, the channel will be closed. It can no longer make any sound! I won't say more about this!
Let's look at the [MAIN] main stereo bus switch.
The sound of the [MAIN] switch control channel is sent to the stereo bus, and if the switch is not turned on, there will be no sound when the fader is pushed to the head. This [MAIN] switch is useful because sometimes we don't want the sound of the channel to go directly into the stereo bus, at which point we can turn off the [MAIN] switch.
[SUB] The sub-marshalle switch sends the sound of the channel to the marshalling busbar! Grouping, as the name suggests, we can group multiple input channels into one group. The marshalled signal is taken from the signal behind the input channel fader, which means that it is the same as the signal level given by the input channel to the stereo bus.
We can use grouping to implement volume control for multiple sources at the same time with a single fader. For example, there is a drum set that uses 8 microphones. We turn on the switches that these 8 channels send to the marshal buses separately. At this point, the sound of these 8 channels all enters the marshalling busbar. Next we'll have the sound of these marshalling buses return to the main stereo bus. The [LEFT] and [RIGHT] switches in the figure. You can specify that the group's sound is sent to the left or right channel of the main stereo bus. Now we can use a pair of groups to control the sound of 8 channels at the same time! Note: Be sure to turn off the sound these 8 channels send to the main stereo bus - turn off the [MAIN] switch. Otherwise we're just superimposing the sound of this drum set onto the stereo busbar!
Figure 11: Marshalling a bus fader and a switch sent to the main stereo bus
An important application of marshalling busbars is that it is very convenient to send the signal of the corresponding channel to the multitrack recorder. In the image above, we can simply press the [SUB] switch to send the sound of the 4th channel to the input of the recorder or audio interface connected to the marshalling busbar to record!
By the way, if you want to buy a mixer for recording production, be sure to choose a product with a marshalling busbar! Otherwise, you can only use assistance, which is more troublesome. Some people have no Dircet OUT direct output or marshalling output on their mixer, and the two poor auxiliary outputs are also responsible for actor return and sending effects. This mixer is not capable of track-splitting recordings. Because if you choose to connect the 2TK OUT on the mixer to the audio interface, the output signal is only the signal from the main stereo busbar, which is mixed with all channels of sound, including the effect sound, so it is impossible to perform track-splitting recording operations!
It is important to note that never turn on the [SUB] sub-marshalle switch from the channel where the audio card returns to the mixer. Otherwise, it may cause a whistling, at least the input sound will be recorded along with the accompaniment from the audio card! This is not a split track recording!
[SOLO] switch and listening busbar.
Guitarists love guitar SOLO, and it's only then that he feels noticed! When recording and live sound reinforcement, the sound recordist also wants to pay attention to the sound of a certain channel. That's when we need to listen to the busbar!
Listening busbars are busbars specifically designed for listening! It has a listening system that directly selects all input and output channels of the listening input channel, the main stereo bus, the marshalling bus and the auxiliary bus. And he doesn't interfere with any channels. It is connected by default on the main stereo bus. When we press the [SOLO] switch of the corresponding channel, the sound will automatically switch to this channel! Listening busbars include pre-attenuation listening to the PFL and post-attenuation listening to the AFL (known in UB1622FX as solo SOLO). The listening bus has its own independent output interface (Ctrl Room OUT) to control the monitor output of the room. This is where we should connect the monitors. In fact, the headphone output is also from the monitor busbar!
Monitor busbars give the tuner a lot of freedom to work. The Monitoring of the Behringer UB Series Mixers is perfect. That's its advantage!
Let's take a look at the system block diagram for this part. Hope to help you understand the above content
Figure 12: Block diagram of the mixer system
Part III: Assist sending and sending return effects
Now let's see how the mixer sends back the actors and adds effects to the sound. This part of the content is always complicated for people who are new to the mixer! It's not that hard! Let's start with the return issue.
It's hard to imagine someone playing without being able to hear the accompaniment and their own instruments! Many friends have had this experience, performing on stage, there are huge speakers at the entrance, but people on the stage can't hear their own performance or singing. Return is to solve such a problem!
Is it okay to directly copy the signal of the main stereo bus to the actor to monitor? Direct use of the signal of the main stereo bus to the actor to send monitoring is only suitable for small personal recording studios, where there is generally only one actor and no worry about feedback whistle problems, and the flexibility of monitoring is very poor. If there are a lot of actors, this practice obviously does not work, because the requirements of the actors are different from the audience! Every actor wants to sing or play at a volume greater than the accompaniment volume, but the sound returned from the main stereo bus is certainly not the case, and some actors may think it is OK but some actors can't hear it. In this case it is impossible for you to make all the actors satisfied. We need auxiliary sound busbars to give each actor a mix of accompaniment notes separately
Figure XIII
The secondary sound bus is independent of the main stereo bus! Its acronym is [AUX]. Each input channel has a knob that sends sound to the auxiliary bus! Take a look at the image above. This is the volume control sent to the secondary bus.
Figure XIV
There are two kinds of auxiliary channels, one is that the signal is taken from the channel fader, which we call "pre-attenuation auxiliary", and the other is that the signal is taken from the channel fader, which we call "attenuated post-attenuation auxiliary". There are two auxiliary busbars on the UB1622FX mixer. Auxiliary 1 can be switched to two states before or after attenuation. Look at the [PRE] switch next to auxiliary 1, we have to press it down to get an attenuated pre-assist. Pre-decay assists are often used to give back to actors. Because we don't have to worry about the actor returning the sound when adjusting the fader, it will become louder or smaller.
Some premium mixers have a lot of auxiliary busbars, so he can give each musician actor a separate mix. Generally speaking, the auxiliary is single-channel! We can certainly do a stereo return with two assists, but only if we have two attenuation pre-assists available!
Another use of the auxiliary is to add effects to the sound of each channel! Let's first understand a concept: the "send back" effect.
In simple terms, the send return effect is to send the sound to the input of the effect, and the effect sound output by the effect is mixed with the original signal, so that we get the sound of the effect!
Some guitar speakers have send "SEND" and return "RETURN" jacks behind them. This is used to join the Chorus, Delay, and Reverb effects. These three effects generally do not connect to the distortion channel of the guitar speaker, otherwise the sound will be difficult to hear. Add effects by sending back and the sound will be better!
A bit off-topic, let's go back to the mixer. What if we want to add reverb effects to a channel? Very easy to do! Remember the insertion point effect mentioned earlier? We can use the insertion point to add reverb or delay to a channel. But if you want to add effects to multiple channels at the same time, you need to insert a reverberation effect for each channel? This is obviously difficult. And even if there are really so many reverberators, it is difficult to create an overall sense of space!
Not so much trouble. We still use auxiliary busbars to do this work, for example we want to add effects to the sound of channel 1. Start by letting channel 1's sound enter the main stereo busbar. Now what we hear is the original sound without any effect. Then we use the auxiliary transmit knob to send the sound signal of channel 1 to the auxiliary bus, the signal output of the auxiliary bus is fed into the effect, and the effect signal is generated by the effect and then returned to the mixer to enter the main stereo bus and superimposed with the original signal. That way we can hear the sound of adding effects! This is a channel case! What if so many channels need to add effects? Don't forget that the auxiliary busbar can be used by any channel that needs to add an effect, we can open the auxiliary knobs of each channel in turn to add the same effect to all channels! And just by controlling the volume sent to the secondary bus, you can add a different amount of effect to each channel! By the same token, the effect sound back to the mixer can also be sent to the auxiliary bus used by the actor's return. This way the actors can also hear the sound with the effects!
It is common to use the fader post-assist to send sound to the effect, which has the advantage that when the channel fader changes, the volume sent to the effect will also change, so that the ratio of the original signal to the effect signal is always the same!
On the UB1622FX mixer there is a channel dedicated to assisting in sending back, AUX RETURN in English. In fact, this AUX RETURN input is a very simplified input channel. It has no gain control, no equalization, and only auxiliary sending. We don't usually use her, but instead return the effect directly to a normal input channel connected to the mixer. The strongest control can be obtained. but! It should be noted that the sound of the effect returning to the channel must not be sent again to the auxiliary bus used by the effect transmission, otherwise it will cause feedback whistling and cause damage to the equipment!!!
We use the following figure to illustrate the application of sending a return effect on the mixer.
Send back the application of the effect on the mixer
Schematic of using auxiliary buses for return and sending return effects. Use a diagram to illustrate the comparison image.
The fourth part: the master part, the main stereo output fader, the monitoring status selection and the auxiliary send return
Let's take a look at the master part of the UB1622FX mixer first! Take a look at the image below
Figure 15: The master part
Volume control for SUB group busbars. As mentioned earlier in this section, the MAIN MIX will not be repeated, which is the attenuator that controls the total volume of the main stereo bus, commonly known as the "main fader". All channels of sound eventually converge here and output from the mixer MAIN OUT. THE MAIN OUT should be connected to the final mix result, such as a tape drive, or to a live loudspeaker that is ultimately given to the audience.
The CTRL ROOM &PHONE knob is used to control the listening bus volume output. Notice that there are three switches on the left side of this knob, namely [TAPE], [SUB], [MAIN]. When the [TAPE] switch is pressed, the listening bus selects the sound from the tape return port, which is used to check the tape return sound. Some advanced card holders support "post-tape monitoring", in this way we can check the sound that has been recorded on tape! If the [SUB] switch is pressed, the subgroup's sound is listened for. If [MAIN] is pressed, the control room listens for sound from the MAIN MIX main stereo bus! Generally speaking, we open this [MAIN] by default.
There is a [MODE] mode switch under the CTRL ROOM &PHONE knob with two states – PFL and SOLO. This PFL means PRE FADER LISTEN, pre-fader listening. It is used to listen for the original state of the input signal. Solo, on the other hand, is actually listening for signals from behind the channel faders. Some consoles are also known as AFL, AFTER FADER LISTEN. The advantage of SOLO is that it can listen to the signal of stereo sound.
AUX SENDS auxiliary send output control knob. Needless to say, of course, is the total output of the control auxiliary bus. As for the STEREO AUX RETURN return input control. I don't want to go into details, because I have already explained the principle of sending a return effect! Through the knowledge of the mixer we have learned, can we understand his mystery? I hope that the latecomers can study it.
Having said all this, I don't know if it will help you. The mixer is a thing that is meant to be used alive. We also prepared a video of the actual operation of UB1622FX. You can learn in conjunction with this article.