Virtual surround sound processor chip QS7779

I was introduced to virtual surround sound technology in 1999. This technology can produce Dolby multi-channel effects with only two speakers. You can feel the sound from the front, back, left, and right. The sound positioning is accurate and you can feel like you are in the scene. It is very wonderful. If you don’t experience it yourself, you can’t believe that there is such sound technology. To be honest, I didn’t believe it before I listened to the QS7779 virtual surround sound processor. I was skeptical all the time. After listening to the QS7779, I was convinced that it was indeed such an advanced sound technology!

Virtual surround sound technology is a signal processing technology that uses the human head sound transfer function HRTF. By decoding the mixed signal of Dolby Pro Logic or Dolby Digital AC-3, the multi-channel signal is subjected to complex calculations using HRTF, and the sound in three-dimensional space is processed according to HRTF, so that the sound entering the human ear conforms to the binaural effect and auricle effect of the human body, and the corresponding sound and image in the spatial direction are produced in the human brain. Therefore, virtual surround sound technology can produce sound with accurate and realistic sound positioning and great live effects with only two speakers, making the audience feel as if they are in the scene. What's even more amazing is that they can feel the sound produced behind them!

Here I would like to introduce to readers the application of the virtual surround sound processing chip QS7779. QS7779 has two types: QS7779CM and QS7779PM. The one with CM in the end is the I2C bus control mode, and the one with PM is the 3-wire serial control mode. Both can be used for parallel control and can be controlled by high and low levels, and the performance effects are the same.

QS7779 is designed by Seponix, a famous American audio company, and manufactured and packaged by NPC of Japan. The chip uses Q-SurroundTM, a top virtual surround sound technology of QSound of Canada, and is certified by QSound Laboratory. The chip can perform 3D stereo enhancement and 3D virtual surround sound processing, and can decode mixed signals of Dolby Pro Logic or Dolby Digital AC-3 and perform 3D virtual surround sound processing. Through a two-channel amplifier, only two speakers can be used to produce a 3D virtual surround sound field that can be compared with Dolby multi-channel.

Figure 1 is the internal circuit structure diagram of QS7779, which is composed of surround sound decoder, 3D virtual surround sound processor, mixer, data input circuit, working mode control circuit, etc.; Figure 2 is the application circuit designed by the author based on the application data of the chip. The center signal can be adjusted through RP1, which can properly adjust the human voice dialogue. The circuit has power reverse connection protection and a three-terminal regulator, which is very convenient for installation in power amplifiers, DVD players, active speakers, multimedia computers, car audio, etc. Due to the three-terminal regulator, the DC power supply can be taken from the DC power supply (+10V-24V) in the machine to be installed. If there is no suitable power supply, a transformer and bridge rectifier filter circuit can be added, but an additional transformer will cause an additional electromagnetic field to interfere with the audio.

In Figure 2, pins 4 and 5 of QS7779 are signal input terminals, pins 17 and 18 are signal output terminals, pin 6 is the center signal output terminal (can be connected to an amplifier to drive the center speaker separately), pin 7 is the center channel signal input terminal (the center signal of pin 6 is input by RP1 in Figure 2), pin 23 is the positive power supply terminal, pin 11 is the power ground, the capacitors of pins 1-3, 19-22 and 24 are external capacitors of the 3D enhancement circuit, pin 15 is the digital control power supply, pin 16 is the mute control terminal, and the mute is effective when the level is high. Pin 13 is the switch control terminal between direct pass and three-dimensional virtual surround sound processing. When the level is high, it is direct pass, and when the level is low, it is the three-dimensional virtual surround sound processing state. Pin 12 is the control terminal for the strength of the processing effect. When the level is low, the effect is weak, and when the level is high, the effect is strong.

The basic features and parameters of QS7779CM/PM are as follows: ① It can decode Dolby directional logic or Dolby Digital AC-3 mixed signals and realize three-dimensional virtual surround sound processing; ② It can also perform three-dimensional stereo enhancement processing on ordinary stereo sound sources (this three-dimensional enhancement effect is better than the three-dimensional enhancement effect of SRS); ③ Working voltage (23) pin: 5 to 13V (typical application 9V); ④ Signal-to-noise ratio dynamic range: 110dB; ⑤ 24-pin SSOP (surface mount) package; ⑥ Input impedance 20KΩ; ⑦ Working current (at 9V): 5mA.

QS7779 has the advantages of simple peripheral components and good surround effect. It is widely used in power amplifiers, car audio, large-screen TVs, active speakers, multimedia computers, VCD players, etc. Interested audiophiles can add the finished board in Figure 2 to their own audio system (installed between the sound source and the power amplifier) ​​to upgrade it to a home theater with two speakers, and enjoy the same virtual surround sound as Dolby multi-channel surround effect!

To bring out the best of QS7779, material selection is also very important! The author's design----① The coupling capacitors for input and output use Japanese high-performance Ruby and Black Diamond capacitors; ② The non-polar capacitors use Japanese Panasonic metalized non-inductive capacitors, or MKP capacitors; ③ The circuit board uses epoxy circuit board and silver plating; ④ The resistors use five-color ring metal film low-noise, and the potentiometers use imported W·L genuine goods; ⑤ Other capacitors use Japanese Ruby, Black Diamond, etc. I believe that the author's material selection is difficult for even the experts in computer modification to start with!

Words are not enough, hearing is believing. The author assembled a set of super-value home theater combination with the circuit in Figure 2 and related circuits and conducted an audition. The configuration is as follows: sound source (Senko AL-P700K Super VCD) → QS7779 → LM4610N (with volume, tone, balance, equal loudness control and 3D processing circuit) → power amplifier circuit (TDA7294 current feedback DC servo type). A Dolby disc "Broken Arrow" was put into the Senko Super VCD. As the plot developed, the three-dimensional sense of space and envelopment was very strong. With the appearance of the plane, wow! A very realistic sense of the scene appeared: I heard the plane flying from the right front to the left rear of myself, and felt the sound effect of the plane flying over my head, which was like being there! At first, I didn't believe it, so I pressed the segment repeat button to listen several times, and then connected the QS7779 to the direct state. I only heard the sound of the plane moving from the right speaker to the left speaker, and the sound effect was very monotonous. Then I connected QS7779 to 3D virtual surround sound processing and continued to listen... The whole viewing process was very realistic, with accurate sound and image positioning, and an immersive feeling. Later, when I added a BBE circuit (XR1071) between QS7779 and LM4610N, I found that the sound positioning was more accurate, very clear, and the sense of presence was better!

I tried playing an ordinary stereo CD. After being processed by QS7779, the clarity and transparency of the sound quality were significantly improved, and its three-dimensional sense of space was very good, better than that of SRS: because SRS combines the difference and sum of the left and right channel signals and the filter characteristics, the enhanced stereo sound will completely lose its directionality and become a stereo mono sound. The three-dimensional stereo enhancement processing of QS7779 is QSound mode - the left and right channels are separated, and the phase difference filter characteristics are used to enhance the three-dimensional stereo effect. The QSound mode's three-dimensional stereo enhancement technology makes the left and right channels highly independent, and there is no additive component of the left and right channel signals, so it can faithfully reproduce the three-dimensional stereo effect of the recording scene.