V700 Stereo Mastering

The wide range phase shifter U790 offers interesing features for the treatment of a mix in an uncommon way. It is for sure that the device cannot be used universally as a mastering equalizer or dynamics processor for all kinds of audio program. However, altering the phase response can result in improvements of a mix that cannot be achieved by another principle. In addition to the modification of the phase shift over a range up to 720 degree between input and output, the device allows to adjust the phase offset between the two stereo channels at the upper end of the audio band.

The Background
According to the general doctrine, human sense of hearing is not able to recognize different phase angles between the input and output of a transmission network. This doctrine is true as far as the phase shift of a sine wave signal is concerned; however, it is definately wrong with complex signal structures. We recognize a particular sound from the addition of the harmonics over the time during the transient phase and not from the static sound. The phase relation between the harmonics is of crucial importance, since any phase shift that is not constant with the frequency alters the relation of the harmonics. Consider that a 1 kHz signal may have a phase shift of 0 degrees while a 3 kHz signal may have a phase shift of 180 degree. Any sound has considerable levels of the third harmonics will be altered by the phase response of the network in a way that the 3rd harmonics is shifted by 180 degrees in relation to the 1st harmonics, if the frequency of the first harmonics is 1 kHz. Apart from the effect of the different addition of the momentary value, the time shift of 0.5 times the period time of the 3 kHz signal alters the transient phase considerably. This must not necessarily cause huge audible effects but it can, depending on the spectral structure of the signal and the phase shift of the network. Phase shift is a lot more audible with transient rich signals than with diffuse sounds, which are not very sensible to such effects.

This makes clear that you cannot expect miracles when using the phase shifter. It is most likely that the effect with diffuse mixes without transients is low or even not existing; however, transient rich mixes can benefit a lot. However, the phase shift must not necesserily result in an improvement. The result of the phase shift depends always on the structure and the spectrum of the mix. Actually the shifter produces the same effect that occurs when you move away from a speaker in a free-field room. 34 cm ~ 1 ft. results in 360 degree phase shift at 1 kHz, but 3600 degree at 10 kHz and only 36 degree at 100 Hz. Due to the total range of 720 degree at 1 kHz, the shifter allows 'moving away' 2 ft. If you try this, please consider that there are acoustic effects that blur the effect of the phase shift if you are not in free-field room.

Phase Distortion of Audio Equipment
Each audio device causes more or less phase shift at the upper and lower end of the audio band. The low frequency range is shifted in positiv direction while the high frequencies are shifted towards negative values. If the devices are not optimized for linear phase response, even a short chain of several units can result in considerable phase shifts that, among other effects, result in 'spongy' bass performance and smudgy highs.

Phase and Stereo
The phase difference between stereo channels will suffer from different phase shifts between the two channels a lot. Little differences of only some degrees in a stereo chain result in a blurred location of the instruments on the stereo base. In difference to the other effects, phase shift between stereo channels is very criticle.

The Phasen Shifter U790
The phase shifter makes possible to adjust these parameters. The stereo phase filter does not alter the frequency response; it just shifts the entire audio band by up to 720 ° at 1 kHz. The phase shift is frequency depending and increaes with the frequency. The control pot covers a range of 180 degrees and a 4 position stepper switch sets the range in steps of 180 °.

Phase Offset Control
The second section of the device allows the regulation of the phase shift between the stereo channel at the upper end of the audio band. The scaling refers to the phase shift at 15 kHz and the phase angle between left and right can be altered by +/- 45 °. This range covers correction of the phase difference as well as effects caused by intendet displacement of the phase.

The Highpass Lowpass Filter with Phase Correction W790 also offers features for phase correction.

Module
The wide range phase shifter U790 is internally and externally balanced and available with electronically balanced and transformer balanced inputs and outputs. The transformer balanced version uses oversized torodial transformers, brand Haufe, Germany. The headroom is more than + 30 dBu thoughout the module and the dynamic range is more than 120 dB_RMS.

The module is hard bypassed as long as the ON swich is not pressed. The U790 is a single slot V700 standard modules that fits into all V700 standard frames.