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blgentry:
--- Quote from: pschelbert on July 30, 2016, 09:27:03 am ---if you upsample from CD (44.1kHz) you need an antialisingfilter just to cut at 22050Hz.
--- End quote ---
Incorrect. If you do straight DA conversion at 44.1kHz you need that filter. If you *upsample* to 88.2 or 174.6, then your filter needs to be at half of the *upsampled* frequency. So 44.1kHz or 88.2kHz respectively. Which are far outside the audible band.
Again, this is why upsampling was invented in DACs. So that the filter would be outside the audible band.
All modern D/S DACs use a filter that's much higher than 22.05 kHz.
Brian.
pschelbert:
--- Quote from: blgentry on July 30, 2016, 10:02:31 am ---Incorrect. If you do straight DA conversion at 44.1kHz you need that filter. If you *upsample* to 88.2 or 174.6, then your filter needs to be at half of the *upsampled* frequency. So 44.1kHz or 88.2kHz respectively. Which are far outside the audible band.
Again, this is why upsampling was invented in DACs. So that the filter would be outside the audible band.
All modern D/S DACs use a filter that's much higher than 22.05 kHz.
Brian.
--- End quote ---
no, as CD has alising from 22050Hz on, if you upsample you generate just multiples (inserting zeros between samples). This has to be filtered before DA conversion, in the digital domain which was the idea to do it in the upsampled DACs. The analog filter can then be very relaxed. Just consult a DSP-book, then you see the effect of just upsampling without filtering. You can do that ss well with software Soundforge, just insert zeros or insert zeros and filter. Observe the spectrum..
Peter
blgentry:
--- Quote from: pschelbert on July 30, 2016, 04:04:05 pm ---no, as CD has alising from 22050Hz on, if you upsample you generate just multiples (inserting zeros between samples).
--- End quote ---
That's not how upsampling works. You don't just "insert zeros". Upsampling generates NEW SAMPLES between the existing samples. If you upsample from 44.1kHz to 88.2kHz, you generate a new sample in between each existing pair of samples. If you upsample from 44.1kHz to 176.4kHz, you generate 3 new samples in between each existing pair of samples.
That's exactly what SoX and other SRC algorithms do when they convert from a lower sampling rate to a higher one. Correspondingly, the aliasing noise is shifted UP to 1/2 of the new sampling rate.
Question for you: Why do you think upsampling is desirable? It's entire purpose inside of DACs is to shift the aliasing noise up. Then you can use a more gentle filter at a very high frequency that is not audible. If this were not true, why would we want to upsample in the first place?
Brian.
flac.rules:
--- Quote from: blgentry on July 30, 2016, 04:33:49 pm ---Question for you: Why do you think upsampling is desirable? It's entire purpose inside of DACs is to shift the aliasing noise up. Then you can use a more gentle filter at a very high frequency that is not audible. If this were not true, why would we want to upsample in the first place?
Brian.
--- End quote ---
Is it? It also reduces noise, which I would say is an important purpose of oversampling.
blgentry:
^ What noise? Aliasing noise?
Brian.
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