# 1-bit DAC

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A **1-bit DAC** (sometimes called **Bitstream converter** by [Philips](/source/Philips_Semiconductors)) is a [consumer electronics](/source/Consumer_electronics) marketing term describing an [oversampling](/source/Oversampling) [digital-to-analog converter](/source/Digital-to-analog_converter) (DAC) that uses a digital [noise shaping](/source/Noise_shaping) [delta-sigma modulator](/source/Delta-sigma_modulator) operating at many multiples of the [sampling frequency](/source/Sampling_frequency) that outputs to an *actual* 1-bit DAC (which could be fully [differential](/source/Differential_signalling) to minimize [crosstalk](/source/Crosstalk)).[1] The combination can have high [signal-to-noise](/source/Signal-to-noise_ratio) and hence an equivalent [effective number of bits](/source/Effective_number_of_bits) as a DAC with a larger number of bits (usually 16–20).

The advantages of this type of converter are high [linearity](/source/Linearity) combined with low cost, owed to the fact that most of the processing takes place in the digital domain, which helps relax the requirements for the subsequent analog [low-pass filter](/source/Low-pass_filter) (for [anti-aliasing](/source/Anti-aliasing_filter#Audio_applications) image frequencies and suppressing high-frequency noise-shaping noise). For these reasons, this design is very popular in digital consumer electronics (CD/DVD players, set-top boxes and the like).[2]

While single-bit delta-sigma DACs have an advantage of a much simpler internal DAC, multi-bit delta-sigma DACs have the advantages of a simpler digital noise-shaping loop, less dithering, a much simpler analog smoothing filter, and less sensitivity to clock jitter, so generally the advantages of multi-bit truncation outweigh single-bit truncation.[3]

## Linearity

Multi-bit DACs may have severe linearity error, mainly due to mismatch in components, with significant error when the [sign bit](/source/Sign_bit) changes (called "zero-crossing distortion"). But a 1-bit DAC only has a gain error, since its transfer function has only full-scale positive and negative reference points, with the intermediate points determined by time averaging. While multi-bit DACs try to seek resolution in amplitude, 1-bit DACs instead compensate by taking advantage of [digital filtering](/source/Digital_filter) combined with the high accuracy in time provided by [quartz crystals](/source/Crystal_oscillator).[4][5]

## Examples

For example, the 1991 [Philips](/source/Philips_Semiconductors) SAA7322/3 [6] first oversamples [44.1 kHz](/source/44,100_Hz) 16-bit input audio by 4x with a low-pass [FIR filter](/source/FIR_filter) to produce a 176.4 kHz intermediate signal, which again oversamples 32x more while adding a 352 kHz digital [dither](/source/Dither) signal, and then oversamples 2x more to produce a 11.2896 MHz 1-bit output (a total of 256x oversampling).

Another 1991 Philips example, the SAA7350,[7] oversamples a total of 384x, which for its maximum input frequency of 53 kHz 20-bit audio results in a 20.35 MHz 1-bit output.

## "Bitstream"

Philips also used the "Bitstream converter" trademark for the TDA1305 [8] which is also an oversampling converter (by 384x), but which ultimately outputs through a 5-bit DAC. So it is not clear that "bitstream" by Philips necessarily refers to a 1-bit output, but could include other DACs that utilize large oversampling into low-bit DACs.

The word "[bitstream](/source/Bitstream)" is also a general computing word for a sequence of bits, used in many contexts other than 1-bit DACs.

## See also

- [Digital-to-analog converter#Types](/source/Digital-to-analog_converter#Types)
- [Direct Stream Digital](/source/Direct_Stream_Digital)

## References

1. Sneep, J.; Kup, B.; Pelser, F.; Dijkmans, K. (1991-05-07). "A bitstream D/A Converter for Top Grade Digital Audio". *1991 IEEE International Conference on Consumer Electronics*. pp. 294–295. [doi:10.1109/ICCE.1991.733197](https://doi.org/10.1109/ICCE.1991.733197). ISBN 0-7803-0001-7. [S2CID 61847063](https://api.semanticscholar.org/CorpusID:61847063). – via [IEEE Xplore](/source/IEEE_Xplore)

1. Smith, Steven W., *The Scientist’s and Engineer’s Guide to Digital Signal Processing* (Second Edition). San Diego CA: California Technical Publishing, 1999 (ISBN 0-9660176-6-8), p. 60.

1. Pavan, Shanthi; Schreier, Richard; Temes, Gabor C. (2017), ["Delta-Sigma DACs"](https://ieeexplore.ieee.org/document/7906224), *Understanding Delta-Sigma Data Converters*, IEEE, pp. 425–450, [doi:10.1002/9781119258308.ch13](https://doi.org/10.1002/9781119258308.ch13). ISBN 978-1-119-25828-5, retrieved 2023-06-30

1. Shah, Prasanna (1991-01-01). ["Audio Magazine (Jan. 1991): Music of the Bitstream"](https://worldradiohistory.com/Archive-All-Audio/Archive-Audio/90s/Audio-1991-01.pdf). *www.gammaelectronics.xyz*. pp. 56–64. [Archived](https://web.archive.org/web/20230330191312/https://worldradiohistory.com/Archive-All-Audio/Archive-Audio/90s/Audio-1991-01.pdf) 2023-03-30 at the Wayback Machine. Retrieved 2023-06-29.

1. ["The Philips Bitstream method: An introduction"](https://www.dutchaudioclassics.nl/The-Philips-Bitstream-method/). *DutchAudioClassics.nl*. [Archived](https://web.archive.org/web/20230302072001/https://www.dutchaudioclassics.nl/The-Philips-Bitstream-method/) 2023-03-02 at the Wayback Machine. Retrieved 2023-06-30.

1. ["SAA7322/7323 Data Sheet"](https://www.hifiengine.info/philips/saa7322-7323.pdf). 2025-08-13.

1. ["SAA7350 Preliminary Specification"](http://www.dalojan.nl/tube/saa7350_bw.pdf). Retrieved 2025-08-13.

1. ["TDA1305T Data Sheet"](https://manuals.lddb.com/DACs/Philips/TDA1305.pdf). Retrieved 2025-08-13.

## External links

- [Care and Feeding of the One Bit Digital to Analog Converter](https://web.archive.org/web/19990225122959/http://www.ee.washington.edu/conselec/CE/kuhn/onebit/primer.htm) tutorial, University of Washington Electrical & Computer Engineering

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Adapted from the Wikipedia article [1-bit DAC](https://en.wikipedia.org/wiki/1-bit_DAC) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/1-bit_DAC?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.