Home Computer Audio Asylum

Music servers and other computer based digital audio technologies.

Converting DSD to PCM

The situation with PCM conversion has substantially changed over the years due to improvements in software and faster processors. This is particularly true where upsampling is concerned. Previously many sample rate programs had gross errors when upsampling 44/24 to 96/24 that were absent in converting 44/24 to 88/24. This is not true with the newer conversion software such as the iZotope 64 bit SRC.

To convert from DSD to PCM you do the following:

1. You treat the 1 bit samples as +1 and -1 floating point numbers
2. You low pass filter these to ensure that there is no aliasing, i.e. no energy remaining above 1/2 the output sample rate. You also have to roll off the high frequencies starting at 25 kHz if your low pass filter hasn't already done this.
3. You high pass filter to remove (or minimize) a DC offset problem arising because the DSD samples can not directly represent 0.
4. You scale the resulting floating point output to numbers in the range of -1.0 and +1.0 and then convert these to 24 bit fixed point (with dither).

There are some other minor issues that have to be addressed such as muting and unmuting at the ends of a file, etc... The choice of filters is where all the art is.

You can use either floating point calculations or integer calculations, provided that you have at least 48 bits of accuracy. The choice depends on the available hardware and its performance. If you do not have enough processing power then you will have to take shortcuts and then you may definitely need to keep things synchronized, i.e. it may not work well at all downconverting to non-integer ratios, unless clever programming is involved.

Tony Lauck

"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar


This post is made possible by the generous support of people like you and our sponsors:
  Crux Audio  


Follow Ups Full Thread
Follow Ups

FAQ

Post a Message!

Forgot Password?
Moniker (Username):
Password (Optional):
  Remember my Moniker & Password  (What's this?)    Eat Me
E-Mail (Optional):
Subject:
Message:   (Posts are subject to Content Rules)
Optional Link URL:
Optional Link Title:
Optional Image URL:
Upload Image:
E-mail Replies:  Automagically notify you when someone responds.