Onkyo VLSC Vector Linear Shaping Circuitry

[rjm]

Onkyo uses a patented circuit to remove noise from the DAC output. They give it a fancy name, "VLSC - Vector Linear Shaping Circuitry" and provide some unhelpful sales-patter to explain how it works.

Conventional D/A conversion methods reduce digital pulse noise at the conversion stage but can't remove it completely. VLSC employs a unique D/A conversion circuit to overcome this problem. Data is converted between sampling points and these points are joined with analog vectors in real time to produce a smooth output wave form. The result—a virtually noiseless, smooth, analog signal based on the digital source that brings out even the most subtle of nuances in music sources (including DVD-Audio and Super Audio CD), DVD Video sources (including high-definition), broadcasts, digital music files such as MP3s, and gaming content.

The original patent (US 6697002) is pedantically titled "Low pass filter" Apparently the device works something like this:

A low-pass filter (700) includes a differential operation circuit (2), a voltage-current conversion circuit (3), and a capacitor (C1). The voltage-current conversion circuit (3) and the capacitor (C1) form a filter circuit (700), and therefore the low-pass filter can remove a high frequency component. The differential operation circuit (2) outputs a differential signal (.phi.C) for the difference between an analog signal (.phi.A) and an output signal (.phi.B). Therefore, with the differential operation circuit (2), a necessary frequency band is not attenuated. The phase level of the output signal (.phi.B) output from the low-pass filter (700) can be substantially equal to that of the analog signal (.phi.A) by the differential operation circuit (2). Therefore, the low-pass filter have a higher attenuation ratio for a high frequency component.

I would upload the patent, its quite interesting, but at 1.5 MB its too fat for diyaudio. You'll have to settle for the main figure referenced by the abstract above.

Anyone with more smarts than me care to comment? Reading the patent it looks like Onkyo are serious about it, but what it actually is, and how different it is from what's been put forward before, is beyond my skillz.

/Richard

[Wolfsin]

I have mulled the meanings of this patent many times over the years. AFAIK it was first used in the INTEGRA Research RDC-7 following a quad of BB1704s. I continue to favor the balanced output of that extraordinary component above all others. How much is the VLSC and how much those DACs?

[SoNic_real_one]

They have a linear integrator included in path, working between each two convesion points. So, instead of steaps, you have straight lines beween conversion points. Linear interpolation done in analogic domanin.

Now is done in digital domanin by oversampling, noise shaping and make use of the output filters to generate the same results or better.

[KlipschKid]

I don't pretend to understand vlsc but I am curious because I have a Onkyo soundcard with the WM8740 DAC and it claims to have vlsc. I assumed the vlsc was the op amp filtering after the DAC ? Each channel has three dual op amps (six dual op amps for stereo) and each signal is fed through five op amps with feedback/filtering. So if that is the vlsc, it seems like it isn't such a dark art ?

[DF96]

Doing this makes the output waveform look superficially more like the original analogue signal, at low enough signal frequencies. At higher signal frequencies it actually increases the attenuation of HF. A 'normal' sample-and-hold DAC output naturally has a sinc frequency response. A 'linear interpolation' DAC has a worse frequency response, with more HF cut. This can be taken care of in the digital filters but why make extra work for yourself, just so that people who like naive pretty pictures are satisfied? The HF droop caused by this does not have an accompanying phase shift, just a fixed time delay, so compensating for it is messy as a normal filter will have both phase and frequency effects. On balance I think it is a bad idea.