Vocal Eliminator

Description: Properly mixed sounds can often be dominated by a solo voice, which may be intentional. If suppression of such a voice is required, the present circuit effectively addresses this issue. The circuit operates on the principle that solo voices are typically located at the center of stereo recordings, resulting in similar voice levels in both the left and right channels. Mathematically, this means that left minus right equals zero, producing a mono signal devoid of voice. However, a challenge arises as the sound levels of bass instruments, particularly double basses, are also nearly equal in both channels. Low-frequency sounds are generally non-directional, and recording engineers intentionally utilize these frequencies to maintain balance between channels. Nonetheless, bass instruments can be retrieved by adding the signals from both channels to the left-right signal. This process is clearly illustrated in the circuit diagram. The incoming stereo signal is buffered by amplifiers A1 and A2, which then feed into differential amplifier A3 and subsequently into summing amplifier A5. Following this, a low-pass filter is implemented using amplifier A6. Users can select between a first-order and a second-order filter by either omitting or including capacitor C2, allowing for subjective audio preference. The low-frequency signal and the difference signal are then combined in summing amplifier A4, with the balance adjustable via potentiometers P1 and P2 according to individual taste. It is noteworthy that the circuit lacks input or output capacitors. While output capacitors can be added without negative effects, input capacitors should be avoided as they would introduce phase shifts that could impair circuit functionality.

The circuit design employs a stereo signal processing approach to effectively manage the suppression of unwanted vocal elements while preserving the integrity of bass frequencies. The buffering stages provided by amplifiers A1 and A2 ensure that the input stereo signal is adequately prepared for subsequent processing, minimizing signal degradation and maintaining fidelity. The differential amplifier A3 plays a crucial role in isolating the center-panned vocals from the mixed signal, leveraging the principle that these vocals will exhibit similar levels across both channels.

The summing amplifier A5 is integral to the reconstruction of the audio signal, allowing for the combination of the buffered signals. The low-pass filter formed by amplifier A6 is essential for attenuating higher frequency components, which may interfere with the clarity of the bass frequencies. The choice between first-order and second-order filter configurations provides flexibility in tailoring the circuit's response to suit specific audio characteristics and user preferences.

The summing amplifier A4 is pivotal in blending the low-frequency and difference signals, enabling a customizable balance that can be adjusted using potentiometers P1 and P2. This feature allows users to fine-tune the output to achieve the desired sound profile, ensuring that the bass response is adequately represented while minimizing the impact of the solo voice.

Overall, this circuit exemplifies a sophisticated approach to audio mixing, effectively addressing common challenges in stereo sound processing while providing users with the tools needed to achieve a balanced and professional audio output. The design considerations regarding input and output capacitors further enhance the circuit's performance, emphasizing the importance of maintaining phase integrity for optimal operation. Otherwise properly mixed sounds often suffer from a predominant solo voice (which might, of course, be the intention). If such a voice needs to be suppressed, the present circuit will do the job admirably. The circuit is based on the fact that solo voices are invariably situated "at the center" of the stereo recordings that are to be mixed. Thus, voice levels in the left- and right-hand channels are about equal. Arithmetically, therefore, left minus right equals zero; that is, a mono signal without voice. There is, however, a problem: the sound levels of bass instruments, more particularly the double basses, are also just about the same in the two channels.

On the one hand low-frequency sounds are virtu--ally nondirectional and on the other hand, the recording engineers purposely use these frequencies to give a balance between the two channels. However, the bass instruments can be recovered by adding those appearing in the left + right signal to the left-right signal.

The whole procedure is easily followed in the circuit diagram. The incoming stereo signal is buffered by A1 and A2. The buffered signal is then fed to differential amplifier A3 and subsequently to summing amplifier A5. The latter is followed by a low-pass filter formed by A6. You can choose between a first-order and a second-order filter by respectively omitting or fitting C2.

Listen to what sounds best. The low-frequency signal and the difference signal are applied to summing amplifier A4. The balance between the two is set by PI and P2 to individual taste. You have noticed that the circuit does not contain input or output capacitors. you wish, output capacitors can be added without detriment. However, adding input capacitors is not advisable, because the consequent phase shift would adversely affect the circuit operation.