American Conservatory of Music
First in High Quality Audio Education

What is Direct Stream Digital?

Introduction

 
Direct Stream Digital is the way in which an analog sound signal is sampled in the digital domain. It was originally invented by Sony for archiving analog master tapes with the idea that they shouldn't be left wondering ten years later why they hadn't used a better encoding scheme before transferring and discarding these masters.  Direct Stream Digital (DSD) is a 1-bit data stream that  represents an analog waveform by a sampling process called delta-sigma modulation at a rate 64 to 128 times that of the audio compact disc rate of 44,100 cycles per second.  Since each bit can have only two values, every bit in a DSD stream only records whether the amplitude of the sound signal was higher or lower than the previous sample. Because the bit-value does not record how much higher or lower the amplitude is, one can imagine that a lot of samples are necessary to accurately reconstruct the input analog waveform signal in the digital to analog conversion process.

DSD Recording produces ultra high frequency noise in the process of recording due to the over and understatement of the ramping voltage changes between samples which are an approximation of the input waveform.  This high frequency noise corresponds to high frequency tape hiss in analog recording formats.  DSD converter design employs noise shaping filters which allow the noise to be pushed to such a high frequency range that the noise becomes inaudible.  The higher the sample rate employed in a DSD recording, the higher the frequency of the noise spectrum.  Therefore, 128 FS DSD recordings have an inherently better analog signal integrity than those carried out at 64 FS.  Because DSD recording captures the analog signal from 20 to 100,000 cycles per second, the recording is much more faithful to the original than digital methods employing pulse code modulation (PCM).  This can be proven with meters and measurements.  Attempts have been made to compare PCM to DSD by subjective criteria thus causing two camps of adherents in the ever growing debate over which format is better.  The Tonmeister Program at the American Conservatory of Music addresses these and other topics with each of its students.  

There are many products that one can choose from to create DSD recordings from vendors such as Korg, Pyramix, Desono (formerly Genex Audio), Sonoma, Meitner, etc.  Although the technology seems somewhat expensive, when compared to Analog professional products, the cost is actually less.  DSD Audio recording offers comparable analog quality in a digital format. For more information about how you may install DSD Audio production capability in your studio or broadcasting station, please write an e-mail to support@dsdaudio.com.  We will be glad to help you with any questions you might have about the technology and its use in your application.