Stereo expansion circuit with unipolar power supply. Stereo expander. How is stereo different from mono?

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. IN Lately stereo expansion devices began 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.

Schematic diagram stereo 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.

02/06/2015 at 12:00

There are many methods for widening the stereo in a mix, all of which together produce excellent results. This includes panning, reverb, various effects, playing with phase, delay between the right and left channels, Mid/Side processing, and even saturation and compression can give us width. There is a lot of controversy about the use of these methods, as the output can be a mess 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 recorded with several microphones, the sound source itself and its surroundings (room) are recorded. With this recording method, there is no need to apply any effects, it is enough to set the required levels, clean and tighten up for readability of the original signal. But when working with already recorded fragments (samples), the picture is completely different. When using samples mixed with room and tails, we do not have the ability to fully control the stereo image of our mix, which gives a very bad result.

In the book " Beatmaker's Bible“I was attracted by the method that sound engineers used before; it consists of dividing the channel into 2, separated 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.

The huge advantage of this method is the preservation of mono compatibility, that is, when listening in mono, the sound is not distorted, but gives good result. You can repeat it in your virtual mixer, but keep in mind that the levels should change strictly in parallel and directly proportional to the amount by which you change the levels of the left channel, by the same amount change the level of the right. (see above)

IN FL Studio There is a plugin that simulates this circuit - Fruity Stereo Shaper. « Fruity Stereo Shaper. A 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 scheme of operation 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 plugin on a snare drum, as it is very difficult to achieve its liveliness and depth, and this is very important, important also for the reason that in the mix you should leave a small margin for vocals in the middle, otherwise they will conflict. I put it after the equalizer, in mode PRE, the way it actually processes the still “dry” sound, I twist the knob PHASE on 90-100% to the left, followed by shifting the channel in the mixer to the left by 5-7% , turning the stereo knob to 100% . It looks illogical, but when these offsets are summed up, you can’t hear it at all, however, the snare drum sounds much wider, without any antiphase. I also route the snare to a send channel with room reverb, which gives even more depth. This plugin 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, handle PHASE all the way left or right, by ear, and I get an even wider sound, but this time for the entire rhythm section. It's important to remember that, the larger the phase shift, the less it is audible and the less its influence on the stereo field. Try, experiment, there are no strict rules in modern production.

What is stereo base? We can call it an imaginary line between two emitters (that is, speakers) of a stereo acoustic system. On the stereo system, participants in the music track being played take a 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 to 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 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.

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. It is when sound wave does not spread in a straight line, but as if covering 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. For a better understanding of what we're 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, and not their entire spectrum, then 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, the low and mid frequencies in relation to the main sound actually play in different time, but since they are separated into channels, our ears hear them separately, and the brain already assembles them into a single stereo image. 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 don’t 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.

Man has gone through a difficult and long evolutionary path in order to gain the ability spatial perception 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: to the left or to 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? Right, different levels volume, 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 - the panorama is not the only way stereo field expansion. 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.