Tuning the rumble of the filter with the expansion of the stereo base. Expansion of the stereo base using the "old-fashioned" method

02/06/2015 at 12:00

There are many methods for expanding the stereo base in a mix, all of which combine to produce excellent output. This includes panning, reverb, various effects, playing with phase, delay between left and right channels, Mid / Side processing, and even saturation and compression can give us width. There is a lot of controversy about the application of these methods, since the output can be porridge or a lot of antiphase, which can make our mix unreadable in certain sources. Of course, when recording live instruments, there is no such problem, as a rule, the sound is picked up by several microphones, the sound source itself and its surroundings (room) are filmed, with this method of recording, you do not need to apply any effects, it is enough to set the required levels, clean and press for readability of the original signal. But when working with already recorded fragments (samples), a completely different picture. When using samples mixed with the room, with tails, we do not have the ability to fully control the stereo image of our mix, which gives a very nasty result.

In the book " The Beatmaker Bible»I was attracted by the method used by sound engineers before, it consists in dividing the channel into 2, spread all the way to the left and right, oppositely duplicated with phase inversion. This method is called " Left minus right”And was used on analog mixers.

A huge advantage of this method is the preservation of mono compatibility, that is, when listening in mono, the sound is not distorted, but gives a good result. You can repeat it in your virtual mixer, but keep in mind that the levels should change strictly in parallel and in direct proportion to how much the levels of the left channel have changed, by the same amount change the level of the right... (see above)

IN FL Studio there is a plugin that mimics this chain - Fruity Stereo Shaper. « Fruity Stereo Shaper... Stereo effect with the ability to separately control the volume of the left, right channels and their inverted copies, as well as their delay and phase shift. Appeared in FL Studio 9 » - Wikipedia... The workflow of this plugin is exactly the same as “ Left minus right", In addition, it has several convenient controls and 2 operating modes - PRE and POST, which imply a place in the processing chain, according to the name of the mode.

I use this plug-in on a snare drum, as it is very difficult to achieve its liveliness and depth, and this is very important, it is also important for the reason that in the mix it is worth leaving a small margin for vocals in the middle, otherwise they will conflict. I put it after the equalizer, in the mode PRE, since it actually processes the still "dry" sound, I twist the knob PHASEon the 90-100% left, followed by shifting the channel in the mixer to the left by 5-7% while turning the stereo knob to 100% ... It looks illogical, but when these offsets are summed up, you can not hear at all, however, the snare drum sounds much wider, while without antiphase. Also, I direct the snare drums to a room reverb send for even more depth. This plug-in can also be used on the group channel of all elements of the rhythm section, after all the processing, for me personally it is: saturation, filtering, compression. After all the processing, I put this plugin in the mode POST, pen PHASE all the way to the left or right, by ear, and I get an even wider sound, but for the whole rhythm section. It is important to remember that, the greater the phase shift, the less it is heard and the less its influence on the stereo field... Try it, experiment, there are no strict rules in modern production.

Man has gone through a difficult and long evolutionary path in order to acquire the ability to spatial perception of the environment. And now, to establish the exact location of sound sources around is an absolutely trifling matter for each of us.

In sound production, with the advent of digital, managing the mix space has become much easier, and now we can immerse the listener in real or completely unfamiliar conditions with the help of speakers or headphones. Well, to the point.

How stereo is different from mono

Unlike mono, where, regardless of the number of channels, the listener receives the same audio information, stereo sound is three-dimensional... That is, it is capable of transmitting information about the location of each sound source: to the left or to the right, closer or further, it moves in space or is static.

In fact, work with a stereo base allows we, the producers, control the size and depth of the created mix, the detail of each individual instrument and increase the drama of what is happening in the track, which not only brings pleasure to the listener, but also facilitates the process.

The principle and methods of realizing a wide sound

The basic principle of working with a stereo mix field lies on the surface. If you carefully read the introductory part of this entry, then you probably already guessed that, by and large, stereo is the difference between the sound from the left and right channels... Besides panning, what can help us make this difference? That's right, different volume levels, psychoacoustic effects, audio delay for one of the channels, mid / side processing and different processing parameters in the channels.

I have already considered psychoacoustic effects separately, so we will not dwell on them in this post.

Let's talk about each of these methods in more detail:

Panning and volume levels

As you probably know, panning instruments in a mix allows you to move them left or right in relation to center. Thus, we can "arrange" sounds around the listener, and in addition, by changing their volume levels, bring closer or remove any of the track's instruments.

Novice producers often rush to the extreme panning positions to create a wide mix, but the result usually sounds unnatural. Therefore, listening to such tracks (especially with headphones) is painful.

Don't go too far - panorama isn't the only way to expand the stereo field. Use it as directed, for balanced positioning sounds.

Sound delay and Haas effect

If you are not too lazy and have read books on the theory of sound, then you should be aware that the presence and size of the delay with which it enters our ears also helps us to determine the position of the sound source.

That is, for example, the sound on the left is "read" by the left ear earlier than the right. The question is literally a couple of tens of milliseconds, but the impact on perception is simply enormous. In many sources, this effect can be found under the name "Haas effect".

You can implement the described technique by duplicating a track with an audio or midi-clip that needs to be processed, panning them in different directions, and delaying one of these clips by about 5-28ms manually or using your DAW. So, in the tracks there is a Track Delay parameter for this.

In an article by Yu. Kuznetsov, M. Morozov and A. Shityakov under this title (Radio, 1985, No. 1, p. 27h; 28), a description of a device was given, which, despite its relative simplicity, could perform two functions at once :

• decrease in the level of rumble;
• improved separation of stereo channels.

At the same time, as shown by the analysis of circuitry solutions, a similar device can be built using a significantly smaller number of passive and active elements. Schematic diagram such a regulator, developed by the author, is shown in Fig. 1.

Main technical characteristics:

• Nominal input voltage, V ..... 0.5;
• Input resistance, kOhm, not less .... 70;
• Voltage transfer ratio .... 1;
• Maximum expansion of the stereo base, times .... 2;
• The level of suppression of low-frequency antiphase components of the roar in the "Stereo" mode (maximally expanded stereo base), dB, at frequencies, Hz: 8. ... .26 (20) 20. .18 (12); 50 ....... 10 (4);
• Harmonic distortion at rated input voltage,%, no more. 0.05;
• Signal to noise ratio. dB, not less ... 80;
• Overload capacity, dB, not less. 20;
• Consumption current, mA, no more. 7.

The device works on the principle of sequential sum-difference conversion of a stereo signal. It consists of a unit for summing the signals of the left and right channels on a double variable resistor R1 and a unit for differential signal conversion on two op-amp DA1 and DA2. In the first, the width of the stereo base is adjusted from the nominal value to zero, the second expands the stereo base by a fixed value.

Serial connection of these nodes made it possible to obtain a device that regulates the width of the stereo base from zero to the maximum value determined by the difference transformation node.

The functions of the roar filter in the described design are performed by the transition capacitors C1 and C2 together with the regulators of the stereo base width R1.1 and R1.2.

In the right (according to the diagram) position of the slides of the resistor R1, the non-inverting inputs of both op-amps are combined, and, therefore, the signals at their outputs are equal in magnitude to the half-sum of the signals of both channels (“Mono” mode).

In the left position of the slides of this resistor, the signals at the inputs of the op-amp DA1 and DA2 are equal to the signals of the left and right channels, respectively, entering the input of the entire device, and the differential conversion unit expands the stereo base to the maximum value. In the intermediate position of the slides of the resistor R1, the voltages at the non-inverting inputs of the op-amp are determined by the expressions: Ul1 \u003d Ul0 (1 - a / 2) + Ul0 * a / 2, Up1 \u003d Ul0 * a / 2 + Up0 (1 - a / 2) at R2\u003e \u003d R1, and the output voltages of the entire device are:

• Ul2 \u003d Ul1 (1 + R / R4) - Uп1 * R / R4;
• Ul2 \u003d - Ul1R / R4 + Uп1 (1 + R / R4);

where R \u003d R3 \u003d R5; Ul0, Ul1, Ul2 (Uп0, Uп1, Uп2) are the voltages of the left (right) channel, acting respectively at the input of the regulator, non-inverting inputs of the op-amp DA1 and DA2, and at the output of the device, and is the relative displacement of the slides of the variable resistor R1 (a \u003d 0. ..1). In particular, when choosing the ratio R / R4 \u003d 0.5 (which corresponds to the maximum expansion of the stereo base by two times) in the middle position of the slides of the resistor R1 (a \u003d 0.5) at the outputs of the op-amp, a stereophonic signal Ul2 \u003d \u003d Ul0, Uп2 \u003d Uп0 and the stereo base has a nominal value.

When deriving the ratios for the voltages acting at the outputs of the regulator, it was assumed that the output resistances of the signal sources of the left and right channels are much less than the resistance of the resistor R1.If this condition is not met, the influence of the output resistances of the signal sources Rg on the operation of the device can be taken into account by formal replacement in the expressions to determine Ul2, Uп2 variable a to a new variable a1 \u003d (a + RgR1) / (1 + Rg / R1).

In practice, the influence of the output impedances of signal sources is reduced to a decrease in the adjustment range of the stereo base in the direction of its expansion, and this influence can be practically excluded by a corresponding increase in the R / R4 ratio.

Figure: 1. Schematic diagram of the stereo base width regulator.

Figure: 2. Printed circuit board of the stereo base width regulator.

In the low frequency region (f<= 1/2пR1C1 = 1/2пR1C2 = ~ 160 Гц) зависимость напряжения гармонического сигнала, лежащих в области частот значительно ниже 160 Гц, напряжения на входах ОУ приближаются к полусумме сигналов левого и правого каналов.

For antiphase components of the roar (Ul0 \u003d -Un0), the transmission coefficient of the device is described by the following expression: К (jw) \u003d Ul2 / Ul0 \u003d Up2 / Up0 \u003d 2jwR1C (1-a) / (1 + jwR1C), where С \u003d С1 \u003d С2; w is the circular frequency of the rumble.

Resistor R2 sets the operating mode of the op-amp for direct current and, together with capacitors C1 and C2, determines the lower cutoff frequency of the frequency response of the device. With the nominal values \u200b\u200bof the elements indicated on the diagram; at the same time, such technical characteristics as harmonic distortion, signal-to-noise ratio, current consumption are determined only by the used op-amp.

Double variable resistor R1 -any, with the control characteristic of group A. The resistance of the resistor R1 may be different than indicated in the diagram, nominal. The capacity of the capacitors C1 and C2 in this case must be changed inversely proportional to the change in the resistance of the resistor R1.

Drawing of the printed circuit board of the device, designed for the installation of MLT resistors (R2 - R5). SPZ-23b (R1), capacitors KM (C1, C2)) is shown in Fig. 2.

A properly assembled device does not need to be adjusted.

It should be noted that due to its low output impedance, the regulator is well interfaced with other functional units of the stereo path.

M. Starostenko. Miass, Chelyabinsk region Radio 1989, 11.

This module is as simple as the MP Harmonic Exciter.

Each band has its own stereo widening control. Level 0 indicates that no extension is applied in the given frequency band. Positive values \u200b\u200bimply broadening, while negative values \u200b\u200brepresent "negative broadening" or channel addition, bringing them closer to the center.

When working with the stereo channel expander, watch the controllers on the right. The horizontal bar is the phase correlation meter (or phase meter), and the "radar type" box below it is the vectorscope screen. Both are used to provide information about the channel separation (or "latitude") of your mix.

Phase Meter

Indicates the degree of similarity or "correlation" (fit) between the left and right channels.

When the sound in the left and right channels is similar, the meter "draws" on the right of this strip. When the left and right channels are the same, then the correlation value will be +1, our meter will be moved all the way to the right.

When the left and right channels are not correlated or very different, the meter walks to the left corner. If the left and right channels are out of phase, in such a situation the correlation is -1, the meter will be completely left. Over time, the phases of the signals in the channels change, but the strip remains colored to give us a picture of the history of correlation changes. A bright white color indicates that the meter has spent more time in this area. Thus, when listening to the mix, you will quickly discover the extremes of phase correlation as well as the most common areas.

Note that you can "zero" the meter by clicking on the bar.

Most of the records have a picture of correlation values \u200b\u200bfrom 0 to +1. Brief spikes to the left are not necessarily a significant problem, but may represent possible mono-incompatibility. You can quickly check the mono-compatibility of phases by clicking on the additional Show Channel Ops options. This menu allows you to get the mix in mono, invert the polarity of the left or right channels, and swap them.

As the stereo widening is applied, the phase correlation will tend to drift towards the left as the left and right channels become "wider" or less similar.

By default, a phase meter is placed at the end of the signal chain so you "see what you hear". A useful side effect of this is that if you mute a range, the phase meter shows stereo correlation only for the band (s) you are listening to.

Vectorscope

Vectorscope also offers visual waveform images.

Typically, the stereo recording drawn in the Vectorscope is usually taller than wide (as shown in the screenshot above). Vertical shapes mean the left and right channels are similar (approaching a mono signal, which is a vertical line). Horizontal patterns mean that the two channels are very different, the mix will sound wider, but this could mean mono compatibility issues.

Options in vectorscope:

You can click on the phase meter to update the picture.

If you want to minimize this display, you can turn it off in the Options Screen menu.

MP Stereo delay

We have kept the most interesting part of the stereo display module for the latest version of the program. Ozone offers stereo delay control, which allows you to adjust the delay between the left and right channels. At first glance, such a delay may not bring a qualitative improvement to the mix, but the use of multiband delay can produce some very interesting stereo effects.

Of course, you know, to make the sound come out from the right you have to increase the level of the right channel. This is true in the sense that the sound on the right side is louder in the right ear. But there is another factor as well. Sound from the right reaches the right ear first. There is a short delay before it reaches the left ear. If you delay a channel by a few milliseconds, you can effectively move the mix sections around the stereo field.

To experiment with stereo display using delays, try moving the delay control knob to the left or right. By default, they are grouped, so they all move together in sync. You should hear how the mix reacts and if you are making a live acoustic recording made with a pair of stereo microphones this can be an effective tool for adjusting the stereo imaging without shifting the channel balance. Thus, latency can be very useful for mastering live recordings. Use it and you will have more experience each time.

This situation is not the only creative use of delay. Click on “Group all band delays” and ungroup the delays. Now you can use the delay between the left and right channels for each band arbitrarily. By moving the delay slider to the right, you will delay the right channel, and to the left, the left channel.

If you expect to hear "echo", you will not hear it. This echo here is very short delay times of 0 to 30 msec. In this time range, you cannot distinguish between two distinct signals, delayed in time as far as you hear the echo.

So what can you do with MT latency? Try moving the bass position using Delay in Range 1. You can move the perception of the bass position without setting the stereo position. Or try shifting Band 3 to the right and Band 4 to the left for a broadening effect. Experiment.

What is stereo base? You can call it an imaginary line between two emitters (i.e. speakers) of a stereo acoustic system. On a stereacoustic system, the participants of the music track being played take a queue. Although, they can stand in line not only on this imaginary line, but also behind it. It all depends on the work of the sound engineer, because he mixes the studio soundtrack. It is clear that the range and clarity of sound depends on the size of the stereo base. The larger it is, the clearer the sound picture opens to us. Unfortunately, our living conditions do not always provide the opportunity to sufficiently separate the speakers from each other. Not to mention the various devices on which the speakers are 15-20 cm apart. In this case, it will become interesting for you to learn about the expansion of the stereo base. The broadening effect is achieved through the cross-addition of the filtered left and right channel signals. It is not worth going into theoretical details, since no discussion can be compared with listening in person.

The first stereo expander circuit

Schematic diagram of a home-made stereo base expander

Main characteristics:

• Input impedance, not less - 70 kOhm
• Harmonic distortion - 0.05%
• Signal to noise ratio - 80 dB
• Current consumption - 7 mA

The first stereo expander circuit is quite simple. This stereo expander circuit is built around two amplifiers and a few other parts. The width of the stereo base can be adjusted with the variable resistor R1. At the output of the right position of the slider, you can get a mono signal, since the stereo base is minimal there. In the left position, the stereo base is doubled.
The stereo base expander circuit is not at all picky about details, although a variable resistor is still better to use a slide resistor. Such a device works well with other parts of the audio path. It can be connected, for example, between a pre-amplifier and a power amplifier. You can power the device for expanding the stereo base using a bipolar stabilized source. The voltage in it is not higher than 15 V.

The second scheme of the stereo base expander

Schematic diagram of the stereo base expander on the TDA3810 chip

Main characteristics:

• Nominal input voltage - 0.5 V
• Input impedance, not less - 75 kOhm
• Voltage transfer ratio - 1
• Harmonic distortion - 0.1%
• Signal to noise ratio - 80 dB
• Current consumption - 6 mA

The second stereo base expander circuit is a little more complicated than the first, since in this one we need a TDA3810 microcircuit. In addition to expanding the stereo base, this part can also receive a pseudostereo signal from a mono one. It works like this: there is a phase shift in both channels depending on the frequency. Let's take a look at the characteristics of this device. First of all, you need to know about its control: you can work with the microcircuit using the switches S1 and S2. Then, when the switches are not closed, the microcircuit transmits the signal unchanged, and at this time the HL1 and HL2 LEDs are off. If both switches are closed, then the effect of expanding the stereo base will take place twice and the LED HL1 will light up. Finally, if only S2 is closed, mono conversion is triggered and the HL2 LED is on.
You also need to know that the stereo expansion device is powered from a unipolar stabilizer source. The stereo base expander circuit will operate in the range of supply voltages from 4.5 to 16 V.