I was thinking when playing PCM through Sigma Delta but pure DSD path would look steppy but much smaller steps since still discrete in time.
Basic technical question about digital source signals
Forgive if this is a stupid question, but the current thread about digital vs analog made me curious: if you look at an analog music signal you see (I think) summations of sine waves i.e. a signal waveform which is "smooth". I realize that there are many contributions to digital sound, but starting with the most basic, if you look at the output from a digital source e.g. on an oscilloscope, would it appear "smooth" i.e. has all the stairstepping that occurs when you convert digital to analog been smoothed out or would the signal appear jagged to some extent?
Thanks for your time.
Thanks for your time.
- ...
- 26 posts total
You can actually see small steps in Stereophile's measurements of many dacs. Playing 24/96 gives much, much smaller steps if the source has the info and the dac has the resolution. Most dacs can only differentiate up to around 20 or 21 bits. 20/96 still has step heights 16 times smaller than 16/44 (and a bit less than half the width). |
So, the quick answer is it is smoothed. Yes, there are discrete samples. But filters reconstruct the analog wave form, essentially via low pass filtering. At the recording studio a similar set of filters is in place to ensure that nothing above the cut-off frequency (let's not get too deep here) is captured -- which can mess up the entire process. Basically this si what a DAC does. It converts Digital to Analog. There are different methods, but step #1 is to create a PDM or PAM output (one's a stair-step, one varies the density of equal height pulses just like fuel injection). The 2nd step is to smooth it out and remove the hgih frequency noise. All of this was figured out int he 1960s, mostly at Bell Labs for long distance telephony. The results are very good, but nothing is perfect. The analog amplifiers and filtering were among the first places addressed for improvement when digital first came out int he 80s. Not only are analog filters in place, but nearly everyone uses digital filters on an over-sampled signal. When you over or up sample a signal the goal is not to magically create missing information from a vacuum. Its simply to move the noise ("steps") to a higher frequency so that they are more easily filtered out. Get i hgih enough and your ear will do it on its own. You can perform normal measurements - noise, distortion, etc on a the analog output of a DAC. G |
headphonedreams You can actually see small steps in Stereophile's measurements of many dacs.Which ones? It's a broken DAC if you can see steps on the output. |
- 26 posts total