What is stereo base? You can call it an imaginary line between two emitters (that is, speakers) of a stereo acoustic system. On the stereo system, the participants in the music track being played take their turn. Although, they can line up not only on this imaginary line, but also behind it. Everything 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 appears to us. Unfortunately, our living conditions do not always provide the opportunity to sufficiently space the speakers from each other. Not to mention the various devices on which the speakers are 15-20 cm apart from each other. In this case, you will be interested in learning about expanding the stereo base. The effect of expanding the stereo base is achieved through cross-addition of the filtered signals of the left and right channels. It is not worth going into theoretical details, since no discussions can be compared with personal listening.

The first stereo expander circuit

Schematic diagram of a domestically produced stereo base expander

Main characteristics:

• Input impedance, no less than 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 using variable resistor R1. At the output of the right position of the slider, you can get a monophonic signal, since the stereo base there is minimal. In the left position, the stereo base expands twice.
The stereo expander circuit is not at all picky about details, although it 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 preamplifier and a power amplifier. The device can be powered to expand the stereo base using a bipolar stabilized source. The voltage in it is not higher than 15 V.

Second stereo expander circuit

Schematic diagram of a stereo base expander on a TDA3810 chip

Main characteristics:

• Nominal input voltage - 0.5 V
• Input impedance, no less than 75 kOhm
• Voltage transfer coefficient - 1
• Harmonic distortion - 0.1%
• Signal to noise ratio - 80 dB
• Current consumption - 6 mA

The second stereo expander circuit is a little more complicated than the first, since in this one we need the TDA3810 chip. In addition to expanding the stereo base, this part can also receive a pseudo-stereo signal from a monophonic one. It works like this: there is a phase shift in both channels depending on the frequency. Let's look at the characteristics of this device. First of all, you need to know about its control: you can work with the microcircuit using switches S1 and S2. Then, when the switches are not closed, the microcircuit transmits the signal without changes and at this time the LEDs HL1 and HL2 do not light up. If both switches are closed, then the effect of expanding the stereo base twice will occur and the HL1 LED will light up. Finally, if only switch S2 is closed, the mono signal conversion is triggered and the HL2 LED lights up.
You also need to know that the stereo expansion device is powered by a unipolar stabilizer source. The stereo expander circuit will operate in the supply voltage range from 4.5 to 16 V.

For stereo playback systems with closely spaced pairs of loudspeakers, it is advisable to use a stereo expansion device. In this case, the subjective perception of the sound picture changes and a spatial impression is created about the localization of sound sources outside the acoustic systems. The sound of cassette and portable radios, tape recorders and tape recorders is improving. Recently, stereo expansion devices have begun to be used even in televisions with stereo playback. The spread of such devices is also facilitated by the fact that Philips has developed a special sound processor to expand the stereo base and create a pseudo-stereophony effect - LSI TDA3810. The devices discussed below use the principles inherent in this successful microcircuit.

The schematic diagram of the stereo base expander is shown in Fig. 10.3. The effect of expanding the stereophonic base (the width of the stereophonic sound picture) is achieved by

Rice. 10.3. Stereo expander

cross-add the filtered left and right channels. The cutoff frequency of the filters of the left and second channels is

is expressed by the relation

As a result, the mid signal is attenuated, which emphasizes the mono sound effect. Input payout coefficient

left channel before its output is

, and the transmission coefficient from the left channel input to the right channel output is negative and equal to

Therefore, below 4 kHz the stereo base

is expanding. Dividers R1R3 (R2R4 in another channel) are necessary so that the signal levels at the input and output of the device are the same.

Rice. 10.4. Printed circuit board and placement of stereo expander elements

All parts of the stereo base expander are placed on a printed circuit board measuring 44 x 41 mm made of fiberglass 2 mm thick (Fig. 10.4). It is best to start installing parts on it by installing two jumpers made of tinned copper wire with a thickness of 0.6...0.7 mm. To avoid problems during setup, before installation, select the expander elements with an accuracy of 3...5%: R1 = R2, R3 = R4, R6 = R7, C2 = NW.

To begin with, it should be noted what a stereo base is, and why is it needed? For me, this is one of the components of high-quality sound. This is the volume of your soundtrack. Any composition mixed in a studio by a professional sound engineer has sufficient stereo amplitude, which gives it liveliness and freedom to fly. The sound becomes more transparent and velvety. This is when a sound wave does not propagate in a straight line, but seems to cover the entire space. And so, we have decided on the concept of a stereo base. But how can you achieve such a sound? Is this quality really only possible when mixing in a studio? No, this can be achieved at home, and in two ways. The first method is software, that is, using plug-ins. The second method is manual, that is, using a panorama and a little trick.

Method one.

Currently, there are many plug-ins and VST instruments capable of expanding the stereo base of a phonogram in one way or another. There is such a wonderful tool called Virtual Guitarist (Fig. 1), which simulates the playing of a live guitarist, in which this function is built-in, and naturally applies only to your own sound. Using the stereo knob, you can either expand the sound or reduce it to mono. If the guitar part in the mix serves as a melody, then it is advisable to make the sound<<шире>>, for more volume and beauty. If the guitar part keeps the rhythm, then the sound needs to be made clearer, and try not to resort to this function.

Fig.1

Fig.2

The CuBaseSX3 sequencer has a built-in synthesizer called Embracer (Figure 2), in which the stereo base can be expanded in parallel with the audio tone. Of all the plugins with which you can expand the stereo base of a phonogram, you can especially highlight the Izotope Ozone mastering package, which copes with its responsibilities in the best possible way. He does this by dividing the individual frequencies of the sound wave across the panorama. It is also possible to equalize the sound using a four-band equalizer. To better understand what we are talking about, let’s look at everything using examples:

Example 1.
This is what a sound wave looks like on the Izotope Ozone diagram when playing pure, unprocessed sound. As you can see in the figure, the sound propagates strictly in the center, and there will be no volume to the ear. If you separate individual frequencies across the panorama, rather than their entire spectrum, the difference will be noticeable even to an inexperienced listener.

Example 2.
This is what a sound wave looks like on the Izotope Ozone diagram when the low and mid frequencies are spread across the panorama by 10% into the right and left channels. In this case, low and mid frequencies in relation to the main sound actually play at different times, but since they are separated into channels, our ears hear them separately, and the brain already collects them into a single stereo picture. The main thing is not to overdo it. If the stereo base of a mix is ​​too wide, it can lose its clarity and dynamics.

Method two.

If you do not have a suitable plugin, you can expand the stereo base manually, using any audio editor with a multi-track recording mode, or you can use any sequencer. The example uses CuBase SX.
First, we need the sound that we will process. Import this track into CuBase (File -> Import -> Audio File). Duplicate the original track, after which we should have it, as in Figure 3.

Fig.3

Next, we take the upper path to the left in the panorama, and the lower one to the right. At the same time, we impose a delay of 10 units on the lower track. But you can deviate from this figure, but the main thing is not to overdo it. That’s it, let’s combine these tracks into one file (File -> Export -> Audio Mixdown), and only in stereo, otherwise the work done will be of no use.

It should be noted that there are basic instruments that need this and those that absolutely do not need stereo phase extension.
Guitar.
The guitar is the instrument that most often undergoes this treatment. This does not depend on the type of guitar, be it acoustic or electric, nor on the style of performance. In rock music, guitar rhythm parts are the basis of rigidity and dynamics, and should cover almost the entire sound area; if it is a lyrical arpeggio part, then the width of the stereo phase emphasizes the beauty and elegance of the melody.
Piano.
Expanding the stereo range of the piano won't hurt, but you can do without it. It all depends on the instrument's place in the mix, and the style of music being played.
Violin players.
It is desirable that the violin sounds<<широко>>, but here everything again depends on the violin part and the style of the musical composition.
Vocals
Backing vocals are subject to mandatory stereo widening, otherwise they will sound like the main voice; by expanding them, we leave room for the lead vocals. But you can hear this treatment on solo vocals as well.
Bass.
It is strictly forbidden to expand the stereo base of the bass guitar, since it is the foundation of the composition and must be strictly in the center, this applies to live styles. In electronic music, everything is possible, for example, expanding the stereo base of the bass is often found in Trance style, since the drum rhythm section is the basis there.
Drums.
Again, in live music they should be strictly in the center; you should only separate the individual components across the panorama.

This module is simple like the MP Harmonic Excitation Device.

Each band has its own stereo widening control. Level 0 indicates that no extension is applied in this frequency band. Positive values ​​imply widening, while negative values ​​represent "negative widening" or summing the channels, bringing them closer to the center.

When working with the stereo channel expander, keep an eye on 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 "breadth") of your mix.

Phase Meter

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

When the sound in the left and right channels is similar, the meter “draws” this bar to the right. When the left and right channels are the same, the correlation value will be +1, our meter will be moved all the way to the right.

When the left and right channels are uncorrelated or very different, the meter wanders in the left corner. If the left and right channels are out of phase, in this situation the correlation is -1, the meter will be all the way to the left. Over time, the phases of the signals in the channels change, but the stripe 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 that area. Thus, as you listen to the mix, you will quickly discover the extremes of phase correlation as well as the most common areas of it.

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

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

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

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

Vectorscope

Vectorscope also offers visual representations of the signal.

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

Options in vectorscope:

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

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

MP Stereo Delay

We have saved 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 any qualitative improvement to the mix, but the use of a multi-band delay can produce some very interesting stereo effects.

Of course, you know, to make the sound come from the right you have to increase the level of the right channel. This is true in the sense that sounds heard on the right side are louder in the right ear. But there is another factor. The sound coming 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 sections of the mix around the stereo field.

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

If you expect to hear an "echo", you won't hear it. The echo here is very short delay periods from 0 to 30 msec. In this time range, you will not be able to distinguish between two distinct signals delayed in time as long as you hear the echo.

So what can you do about MP latency? Try moving the position of the bass using the Delay in Band 1. You can move the perceived position of the bass without setting the stereo position. Or try shifting Band 3 to the right and Band 4 to the left for a treble extension effect. Experiment.

Man has gone through a complex and long evolutionary path in order to gain the ability to spatially perceive the environment. And now establishing the exact location of sound sources around is an absolutely trivial matter for each of us.

In sound production, with the advent of digital, managing the space of mixes has become much easier, and now we, using speakers or headphones, can immerse the listener in real or completely unfamiliar conditions. Well, let's get down to business.

How is stereo 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: on the left or on the right, closer or further, moving in space or static.

In fact, working with stereo base allows We, 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.

Principle and methods of realizing wide sound

The basic principle of working with the stereo field of a mix is ​​obvious. If you carefully read the introductory part of this entry, you probably already guessed that, by and large, stereo is the difference between the sound from the left and right channels. What can help us make this difference besides panning? That's right, different volume levels, psychoacoustic effects, sound 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 of center. Thus, we can “arrange” sounds around the listener, and in addition, by changing their volume levels, bring closer or remove any of the instruments of the track.

Beginning producers often rush to pan sounds to extreme positions, hoping to create a wide mix, but the result usually sounds unnatural. Therefore, listening to such tracks (especially on headphones) is painfully difficult.

Don't go too far - panorama is not the only way to expand the stereo field. Use it for its intended purpose, for balanced sound positioning.

Audio delay and the Haas effect

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

That is, for example, a sound on the left is “read” by the left ear earlier than by the right. It’s literally a matter of 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, on the tracks there is a Track Delay parameter for this.