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pschelbert:
--- Quote from: sorepinky on July 26, 2016, 08:31:12 pm ---Given the credibility of some of your other source material, it isn't entirely surprising that the Wikipedia page commences with "This article's factual accuracy is disputed".
This thread is about SoX resampling.
For example, the 9018 ESS Sabre DAC supposedly takes all PCM sources, no matter what their sample rate, and upsamples to 84.672MHz. How can MC's upsampling from say 44.1kHz using SoX's algorithms to 176.4kHz make an audible difference compared to using SSRC's algorithms, when the DAC will upsample 480 times higher to 84.672MHz anyway?
I only ask because after a few weeks listening, I kind of think with SoX the sound is pretty good.
--- End quote ---
Hi
all the Sigma-Delta DAC do convert the PCM to a very fast 1 or 4-5bit serial bitstream. They need antialising filters. As I said in this thread, this antialising filter can be moved out to higher frequency (2-4x only in most DACS, limit often is 192kHz sample-rate). The point is, if you want to get rid (mostly) of the effect of this filter in the audible range, you upsample with SOX or other tool and introduce your own antialising filter which introduces the changes you want or prefer (amplitude and phase, time smearing. There is no way to do any "perfect" filter though. There are just theoretical limits (up to now nobody jumped over his shadow...). Its just a trade-off. And yes its not clear if you can do any better than the professionals like AD, TI, AKM, ESS...
The nice thing its just software, no soldering or hardware changes needed.
SOX is for sure a great algorithm.
Peter
blgentry:
--- Quote from: pschelbert on July 27, 2016, 04:06:55 pm ---all the Sigma-Delta DAC do convert the PCM to a very fast 1 or 4-5bit serial bitstream. They need antialising filters. As I said in this thread, this antialising filter can be moved out to higher frequency (2-4x only in most DACS, limit often is 192kHz sample-rate).
--- End quote ---
This isn't the place to discuss it, but you're just wrong. Antialiasing filters far above the audible band aren't audible. That's why oversampling was invented! But I won't post about this here any more if you won't. If you want to discuss it, maybe we should start another thread.
Brian.
BillT:
I thought over sampling was invented to improve the performance of DACs.
Back in prehistory and the start of CD, the original Philips idea was to use a 14 bit system, which was entirely adequate for domestic audio and easier to produce. Sony wanted a bit of wiggle room with a 16 bit system. In the end a 16 bit system was developed between them, but could be used with lower resolution DACs.
Sony could make 16 bit DACS, Philips could only make 14 bit DACs but they had clever engineers who worked out an oversampling system which could deliver 16 bit performance from a 14 bit DAC.
The largely pointless bigger number race has continued ever since.
blgentry:
When I said "oversampling" I meant converting the input sample rate (44.1kHz for CD) to a higher sample rate like 88.2 or 176.4kHz. That technique (upsampling or overampling) was invented to shift the aliasing frequency FAR outside of the audible band, which allows a more gentle low pass filter at frequency way outside the range of human hearing.
Brian.
pschelbert:
--- Quote from: blgentry on July 27, 2016, 06:22:33 pm ---This isn't the place to discuss it, but you're just wrong. Antialiasing filters far above the audible band aren't audible. That's why oversampling was invented! But I won't post about this here any more if you won't. If you want to discuss it, maybe we should start another thread.
Brian.
--- End quote ---
Hi
if you upsample from CD (44.1kHz) you need an antialisingfilter just to cut at 22050Hz. This is a steep filter which must not damage anything in the audible range 20-20000Hz (passband). So thsi filter is very close to the audible range. There are no doubt other filters in the DAC which are way highter than audible range.
Such a filter is implemented in SOX, which in turn is adjustable (its in the SOX command line version).
I understand its only for experts, may be not really adequate here, and I understand it will not be soon implemented.
Peter
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