1-bit audio

1-bit audio, also trademarked as Direct Stream Digital (DSD) is a representation of digital audio as a stream of 1-bit digits, typically produced by use of a Sigma Delta Modulator (SDM). For an overview of the technique, we refer to Reefman and Janssen (2003).
For our intentions of observing the erosion processes of digital audio representations, 1-bit audio has the wonderful property that each bit of information has the same significance. Note that this is different from a multi-bit-word (PCM) representation where the loss of a bit has different effects depending on its position in a data word.
We are experimenting with representations of 1-bit audio on various physical information carriers, in electromagnetic or visual state. Specifically, we are working on printed or laser-engraved bit streams on various materials, then subjected to degradation processes.

Printed 1-bit audio representation on paper, analogous to a bit stream on a Compact Disc (CD).


Zooming on the 1-bit audio track. The bit stream spiral starts above the image center.


Degraded print potentially also results in degraded audio quality.


1-bit audio: Testing audio hardware

For an upcoming performance at the Ars Electronica Festival 2020 SOUND CAMPUS, we are testing hardware to interconnect 1-bit audio streams.

For that purpose, we are using an STM32F4 Discovery Board to generate 1-bit audio streams, sent through a Future Sound Systems MTX9 point pin matrix (Figure 1) as often found in modular synthesis systems.

The software used on the STM board to efficiently generate 1-bit audio streams using DMA transfer over an SPI interface is an offspring of our DADA hardware development efforts.

Figure 1: Testing Future Sound Systems MTX9 with high-bandwidth audio signals

The FSS MTX9 can be used as passive hardware (only 1-to-1 connections), or using the MTX9A buffer board to sum over input busses.

In passive mode (Figure 2), the bandwidth is sufficient to come close to 1 MHz bit rate which allows 32-fold oversampling at usable PCM audio rates.

Figure 2: Oscilloscope screenshot of MTX9 output (purple) against 1-bit audio input (turquoise) at around 500 kHz bit rate

For active mode (using the buffer board MTX9A, Figure 3), the hardware introduces low-pass filtering, reducing the audio bandwidth to around 100 kHz. This is good enough for high quality analog audio, but not for 1-bit digital audio at high bit rates.

Figure 3: Oscilloscope screenshot of MTX9A output (purple) against 1-bit audio input (turquoise) at around 100 kHz bit rate

Clearly, it must be noted that the summing function over inputs is not strictly meaningful for 1-bit signals, where some kind of post-processing needs to bit applied to return to single bits.

Printing new 1-bit audio object “Reference Tone”

For the upcoming exhibition UNDERSTANDING ART AND RESEARCH at the Museum of Applied Arts (MAK), we today printed the new prototypical audio object Reference Tone at the Digital Photography Lab at the University of Applied Arts.

It is a variation on the large-scale 1-bit audio print concept, similar to Midnight Song, as exhibited in our Auditorium of Rotting Sounds. Reference Tone represents a 1 kHz -3 dBFS sine tone at 44.1 kHz PCM sample rate, converted to a 1-bit DSD encoding with 64-times oversampling.

The director of the lab, Josef Schauer-Schmidinger supervised the printing of the 250 MB programmatically generated PDF file at 150 dpi bit structure size. The printed diameter of 100 cm contains approximately 30 Million bits, equivalent to about 10 seconds of very high quality audio.

1-bit audio printing at the University of Applied Arts Vienna

Today, we visited the gravure printing workshop at the Institute for Graphics and Printmaking at the University of Applied Arts in Vienna. The staff around Veronika Steiner and Attila Piller showed us their printing procedure and the possibilities in terms of materials, size and achievable resolution.
Obviously, one of the important limiting factors is the quality of the rasterization which is usually done with a laser printer on transparent film. This film is used to expose the polymer printing plate with ultraviolet light. The non-exposed parts of the plate are washed away, making room for the print color.

On our quest for maximum resolution of the photomaster, we also visited Josef Schauer-Schmidinger at the workshop for Digital Photography. Although they specialize in digital photography, we will have the possibility to reproduce large-scale high-resolution ink prints (160 cm width) onto 8″x10″ film with an analog Sinar camera, once their darkroom is installed in a few weeks. The target resolution should be more than 2400 dpi.

1-bit audio laser engraving

Today, we have gained new knowledge about laser engraving thanks to the great guys at Universal Laser Systems Vienna.
The laser engraving expert convinced us that a target resolution of 1000 dpi is not easily attainable due to restrictions of laser focus, positioning accuracy and, above all, material constraints.
Nevertheless, we will research further in this direction, since laser engraving allows the application of visual representations of audio on various interesting materials.