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What is DSD Audio? 10 Things You Want to Know [Guide for Beginners]

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Audio Basis - educational articles

Audio DSD (Direct Stream Digital) is format to record sound ♬ in high resolution. Read about sound quality ► players ► converters ► file formats ► editing ► other issues.

The format is based on 1-bit sigma-delta modulation. Multichannel music is supported.

What is DSD Audio?

 

1. Bit depth and noise level

 

DSD audio is next generation of high resolution formats after CD to improve signal/noise ratio in audible band.

DSD music file formats: SACD ISO (ripped dsd albums from SACD) and DSF, DFF, CUE+DSF/DFF.

As rule, DSD have bit depth: 1-bit. And quantization noise energy have significant level.

However, for DSD, so-called noise shaping of spectrum is used. And quantization noise energy is re-distributed. Most the energy are pushed from low to high frequency range, out of audible range (above 20 kHz). That functionality implemented in sigma-delta modulator.

 

Noise shaping of 1-bit DSD signal (spectrum)

Noise shaping of 1-bit DSD signal

 

This noise have level comparable with musical signal.

When the DSD record is played back, low frequency filter cut the noise. It is implemented in sigma-delta demodulator.

 

DSD decoder (demodulator)

DSD decoder

 

Therefore, at spectrum noise level into DSD's audible range is comparable with PCM one.

Also DSD may be implemented in bit depth more 1. Read details below.

 

 

2. Sample rate

 

DSD use standard range of sample rates based on 44100 Hz:

  • DSD64     = 44100 *   64   =   2 822 400 Hz =   2.8 MHz
  • DSD128   = 44100 *  128  =   5 644 800 Hz =   5.6 MHz
  • DSD256   = 44100 *  256  = 11 289 600 Hz = 11.3 MHz
  • DSD512   = 44100 *  512  = 22 579 200 Hz = 22.6 MHz
  • DSD1024 = 44100 * 1024 = 45 158 400 Hz = 45.2 MHz
  • Etc.

Also 48000 kHz base is possible. There are not technical limitations for the sample rate value. But compatibility issues are very probable.

 

 

3. Noise, Maximal Level and Stability Issues

 

When sigma-delta modulator is designed, the engineers pay attention to:

  • noise level in audible range and
  • tolerance to overload.

To solve these issues the engineers have:

  • bit-depth,
  • sample rate,
  • noise shaping.

 

These parameters should be considered in complex.

 

Bit depth

Bit depth reduce noise level as itself due lower quantization error.

 

Noise shaping

Noise shaping "push" the noise energy out of audible range.

We can suggest that more noise energy may be pushed out of audible range in sigma-delta modulator. But it demands more steep noise-shaper.

Steeper noise shaping can cause higher probability of glitch (broken stability) of sigma-delta modulator.
After glitch, silence or some oscillations are generated at output of sigma-delta modulator.
After broken stability the modulator should be forcibly reset.

Overload tolerance of DSD-modulator

Overload tolerance of DSD-modulator

 

Sample rate

Higher sample rate reduce noise level due distribution of noise energy into wider band. Also it give ability to use sloper noise shaping.

Energy is square of figure, concluded between spectrum line and horizontal axis into band ([sample rate] / 2).

 

Sample rate and quantization noise level

Sample rate and quantization noise level

 

At the left and right pictures squares of the noise energy figures are same. But figure, that wider in X-axis, have lesser level.

It allow push more noise out of audible band and easier keep stability.

 

Resume

We can see that lower noise and higher stability to overload can be achieved different ways.

As example, better quality is noise shaping implementation matter for same bit depth and sample rate. But we can increase sample rate or bith depth to decrease noise level for unchanged noise shaping.

 

 

 

4. DSD in figures

 

Pro audio modulators have level noise in audible frequency range for sample rates (read details):

  • DSD64 about -125 ... -145 dB (comparable with PCM 24 bit)
  • DSD128 about -165 dB (better than PCM 24 bit)
  • DSD256 and higher about -170 ... -200 dB (comparable with PCM 32 bit)

Noise level in the audible frequency band almost don't depend on demodulator. But noise should be maximally suppressed out of the band. Ultrasound noise can cause audible intermodulations distortions.

 

Read more about DSD vs. DSF vs. DFF >

 

 

5. DSD vs. PCM

 

DSD is like to PCM, but quantization noise spectrum is shaped for decreasing noise into audible range.

We can apply noise shaping for usual PCM. But difference here is band reserve for pushed noise out of audible frequency range.

 

DSD vs. PCM (multibit)

DSD vs. PCM

 

PCM have lesser reserve (above audible range) than DSD, but PCM have higher bit depth.

Noise shaping for PCM is implementation matter too, like DSD.

Therefore, no advantages either PCM or DSD format as itself. But implementation makes difference.

DSD decoder (demodulator) is 2-position (1 / -1) voltage generator and low frequency filter. It is simpler than PCM hardware demodulator. Because PCM demodulator contains several DSD decoders or multi-voltage matrix. So we have more abilities to make cheaper DSD DAC better than PCM one.

 

Read more about DSD vs. PCM >

 

 

6. File formats and compression method

 

  1. DSD in audio was applied on optical disks SACD (Super Audio CD).
  2. DSD contains into files DSF, DFF, SACD ISO (SACD disk image).
  3. WAV, FLAC as DoP (DSD over PCM) container.

SACD disc may be losslessly converted to SACD ISO [1], [2], [3].

SACD ISO image may be extracted to DSF and DFF files. The extraction may be applied

Read more about DSF and DFF.

1-bit audio files (DSF, DFF, SACD ISO) and disks may be either uncompressed or compressed with DST method.

DoP is open protocol that allow pack DSD as PCM for compatibility with software and hardware [4]. The PCM cannot be played as PCM.

 

Also DSD may be streamed via network.

Uncompressed DSD64 demands capacity 2.7 Mbit/sec = 44100 Hz * 64 / 1024 / 1024.

 

DSD sources

DSD sources

 

Also index file CUE + DSF/DFF audio files may contains dsd album.

 

 

7. DSD players

 

DSD audio players (hardware and software) is able to playback all or some of DSD file formats. Stereo player may downmix multichannel to stereo. As alternative multichannel files may be pre-converted to stereo. It allow to save space on hard disk of audio player. Downmix is lossy audio processing. Its quality defined by implementation.

Read more about DSD players here >

 

 

8. DSD converters

 

DSD converters perform:

Read more about DSD converters here >

 

 

9. DSD editing software

 

DSD editing is sophisticated issue due modulation noise. Non-linear processing can cause audible intermodulation distortions (noise).

Currently no information, that is known for author, about "native" DSD processing (example: gain altering, resampling, etc.) without conversion DSD to PCM and PCM to DSD back. Except, merging/dividing audio file.

 

 

DSD editing

DSD editing

 

PCM here may be considered as "multibit DSD". PCM is not obligatory mean "24 bit / 352 kHz" or so on. Author recommend use 32- or 64-bit float point bit depth. This PCM contains high frequency modulation noise. But for conversion this "multibit DSD" to 1-bit DSD need re-modulation with noise shaping.

Losses of editing with DSD-PCM conversion is comparable with resampling.

Recording studios may distribute DSD records without editing.

There is DXD format. It is PCM (as rule "24 bit / 352 kHz" or so on) with high sample rate and bit depth and legacy DSD noise. However the noise can cause audible intermodulation distortions. Before non-linear processing, the high frequency noise cutting is recommended.

Video: Looks to experiment with cutting ultrasound noise

 

 

 

10. DSD audio samples

 

DSD audio samples may be downloaded here:

  1. Demo tracks #1
  2. Demo tracks #2
  3. Test simple signals

 

 

Conclusion

 

DSD is 1-bit audio data format for hi-fi audio.

For same sample rate and bit depth DSD may have different quality, that depend on implementation.

DSD digital-to-analog converter is simpler than PCM one. It allow to get better quality simpler way.

DSD may be edited via DSD to PCM and PCM to DSD conversion. The edition is lossy, except merging/dividing.

 

 


Read more about DSD

  1. DSD vs. PCM. Real competitors? >
  2. DSF vs PCM. What is common base? >
  3. DSD Decoder Audio >
  4. How work sigma delta modulation in audio >
  5. DSD Converter of Audio Files: What Inside? >
  6. What is Audio Formats DSD 2.8 DSD64 DSD5.6 DSD128 DSD256 DSD512 DSD1024 >
  7. DSD vs DSF vs DFF Files Audio. What is difference >

 

 


References

  1. SACD ISO ripping (way #1)
  2. SACD ISO ripping (way #2)
  3. SACD ISO ripping (way #3)
  4. DoP specification

 

 


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