- Asynchronous Reclocking
- Output Stage
- Error Correction vs. Jitter
- Slaving Computer Soundcards
- Battery for Digital Schematics?
- Stacking Multiple Converter Chips
- Benchmark's UltraLock
- Digital Filtering
- One-box CD Players
- Synchronous Reclocking
- Jitter Sources
- Large Buffer
- Disbelief in LessLoss
- A/D Converters
- Sampling Rates
There is nothing mentioned [on the LessLoss website] regarding the filter function utilized with the oversampling. And I personally think that is far more important than the broad brush comparison of non-oversampling and classic oversampling. Most oversampling filters are windowed "sinc" filters, which blur time-domain resolution compared to non-oversampling DACs. But if [LessLoss] uses a more-time-resolute filter, the DAC could strike a happy medium between the time-smear of oversampling and HF modulation of non-oversampling.
Our experience with filtering techniques is based on the following experimentation (after having clearly asserted that the PCM1704 was the converter of choice):
1. No Oversampling. We used second and sixth order analogue filters in several configurations including solutions with transformers etc. after the DAC chip.
2. With Asynchronous Upsampling (When the Upsampling is synchronous, i.e. all timing comes from the same generator, this would be in effect the same thing as oversampling). In this case we used Asynchronous Upsampling, meaning that there were two master clocks involved. We used the CS8420 and the AD1896A (best on the market today) chips.
3. With Synchronous Upsampling. (this time with everything timed off of the same generator, so in effect this is oversampling). We used the CS8420 and the AD1896A chips.
4. Using the Oversampling filters DF 1704 and DF 1706.
5. Using the Oversampling filter SM 5847 (best mass-manufactured on the market today).
6. Using the Oversampling filter PMD100 (good, but works only with 44 and 48 kHz).
7. Using Upsampling to 96 and 192 kHz calculated via computer processing.
Our experience using all of these methods is as follows (some of this is subjective as a matter of course):
1. Both Upsampling and Oversampling always resulted in better sonic resolution and detail than without the upsampling.
2. Without Upsampling or oversampling the sound is perhaps 'softer', but the obvious presence of intermodulation distortion results in a more 'muddy' or 'non-detailed' sound.
3. The SM 5847 filter sounded better than all the others except the one we emulated using a complicated algorithm on a computer.
4. The DF 1706 sounded almost exactly the same as the SM 5847, but is much more efficient (uses much less power from the power supply). This means that it also adds much less pollution back into the power chain. For these reasons we utilize this filter in the DAC 2004.
5. We were dismayed by Asynchronous Upsampling. It was unpleasant to listen to the 'muddy' sound and the interpolation or other such by-products of frequency beating. This was especially audible when we switched to clean balanced battery power.
6. CS 8420 should not be used at all. The sound was simply bad.
7. This aspect is perhaps the least known amongst audiophiles today. Oversampling filters are VERY sensitive to Jitter. If, for example, you have a low-quality transport as digital master and an external DAC which uses oversampling as digital slave, then in this case, oversampling is guaranteed(!) to lower the fidelity of the sound. Where this solution really shines is when there is almost no Jitter. In this special configuration the DF 1706 does truely represent the highest quality attainable by known methods.
8. Now, for the absolute utopian wish-list, it is probable (but not yet proven either correct or incorrect) that a better oversampling filter could be realized by using DSP processors like the Analog Devices "sharc" processors or similar. However, this would be difficult to realize at the price level we are selling at. Also, it is probable that the sound quality improvement would be considerably less than present sonic differences between certain copies of the same CD material.