Wading into it

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One of the more confusing aspects of digital audio is the two formats we have to deal with: PCM and DSD. PCM stands for Pulse Code Modulation and DSD stands for Direct Stream Digital. The first acronym, PCM, actually describes the format while the second acronym, DSD, is a marketing term invented by Sony and Phillips (DSD is more accurately titled PDM). So, the two formats are PCM and PDM, both acronyms that describe to us engineering types what they do and how they do it. I know, I know. Several of you have written me begging that I explain "in english" and not use acronyms that confuse. How about this as a compromise? Would it help if I refer to PCM as simply Multi-Bit Audio, and DSD as Single-Bit Audio? Let's try that and see if that helps. I'll include the acronyms in parenthesis for a while to help clear the way. Multi-Bit Audio (PCM) is the standard digital audio we all grew up with, starting with CDs introduced in 1982. In later years Multi-Bit audio gained more bits and ran faster, creating what has become known as High-Resolution audio. But it's still Multi-Bit Audio. CDs are Multi-Bit Audio with 16 bits and running at a speed of 44,000 times a second. High Resolution audio has an added 8 bits for a total of 24 and a speed of anything more than 44,000 (although generally 88,000 would be considered minimum). The basis for this format has been around for decades. Single-Bit Audio (DSD or PDM) first came to our attention 17 years after the introduction of the Compact Disc, in 1999, in the form of the CD's intended successor, the SACD (Super Audio Compact Disc). SACD is another marketing term that describes a DVD disc running Single-Bit Audio. Unlike Multi-Bit Audio, Single-Bit only has one bit but runs at a considerably faster speed, 2,800,000 times a second (standard DSD) or double that at 5,600,000 times a second (double DSD). The basis for this format has been around for decades as well. Multi-Bit Audio (PCM) is a type of code that is meaningless when you look at the code with your eye. To decode and play it back you need a computer or a dedicated IC that can unravel the code before it gets turned into music. Reasonably complicated. Single-Bit Audio (DSD) actually looks like the music it is playing. To decode and playback Single-Bit Audio all you need is a simple analog filter and out comes music. Simple. I found this graphic for you, showing what it takes to record music to each format with an A/D Converter. It's very simplified, but you get the idea. Note how much more "stuff" is required to convert analog to PCM. Tomorrow we wade in a little deeper. DSD_vs_PCM2
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Paul McGowan

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