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What is DSD Audio? [Sound Quality, DSD vs PCM]

Audio Basis - educational articles

yuri korzunovProbably, you already read articles, that explain DSD audio (Direct Stream Digital). But it may not easy still understand why 1-bit-only DSD may successfully compete with multibit PCM.
Read simple explanation what is DSD exactly and how it works, its sound quality, DSD vs PCM, myths debunking and other essential issues by audio software developer Yuri Korzunov.


What is DSD

What is DSD Audio? Explained

DSD (Direct Stream Digital) is an audiophile high-resolution audio format. It is a method of a coding analog signal to digital form via sigma-delta modulation. It's alternative to PCM (Pulse Code Modulaion), that used in CD-audio, WAV, FLAC, mp3 and other formats.

Digital form of an audio signal is number sequence.

PCM is sequence of measured values of an audio signal.

DSD and PCM difference
DSD and PCM difference

In sigma-delta modulation (a.k.a. DSD) each number (1-bit) show positive or negative level altering relative previous sample. And, as rule, DSD is explained as a saw (level grow or fall) between samples. But, it did not give easy understanding of basical DSD principle. Below we'll consider the easier explanation.

Read:

  1. How DSD works...
  2. About sound quality comparison with PCM...
  3. DSD and PCM DAC.

 

Watch and share: What is DSD audio? Video explanation
 

 

 

DSD history

Audio CD optical disk (PCM modulation / PCM format) was one of first digital formats. It was a source with low distortion and noise level comparing analog ones. I think, now many people forgot what is "real analog noise".

From CD (PCM) to SACD (DSD)

From CD (PCM) to SACD (DSD)

 

After CD, demands to sound quality improvements could be implemented by increasing sample rate or bit depth.

 

Audio quality (sound quality) is a level of noise and distortions, that cause format/software/equipment. The level may be normalized by psychoacoustic criteria.

 

However, Sony and Phillips decided to use another kind of modulation - 1-bit sigma-delta modulation. At first glance, using of 1-bit is impossible, because such bit depth (resolution) causes huge noise level. But, if high sample rates are used, noise energy may be pushed out of audible frequency range (to ultrasound). That action is called "noise shaping".

Practically, 1-bit conception may be easier, than multi-bit, in a DAC implementation (read below).

When DSD music is converted to analog, ultrasound noise is filtered.

Medium, that contains 1-bit DSD audio stream was called SACD (Super Audio CD).

Look at DSD file infographic >

 

DSD features

DSD features
Abbreviation of:  Direct Stream Digital
Audio data coding method: sigma-delta modulation (details and video)
Bit depth: 1 bit or more (details about sound quality)
Sample rate: DSD64 (2.8 MHz), DSD128 (5.6 MHz, double), DSD256 (11.2 MHz, quad), etc. (details)
Channel number: Stereo or multichannel
Medium: SACD optical disk, including hybrid SACD (with CD layer), computer files [SACD ISO (ripped albums from SACD) and DSF, DFF, CUE+DSF/DFF] (details)
Specification: "Scarlet book" (1999)
Applications: Music production, home hi-fi/hi-end audio

Direct Stream Digital is one of high resolution audio formats to improve CD-audio dynamic range in the audible band.

Read below about sound quality issues (noise, bit depth, band, sample rate, DSD versus PCM).


 

How DSD works?

As rule, DSD has explained in the time domain: positive samples increase level, but negative decrease and analog filter smooth "saw" form of signal.

DSD and PCM | Time domain

 

 

Into DSD analog-to-digital converter (ADC), measuring "saw" signal is compared with input analog signal.

DSD and PCM difference
How DSD ADC works

At the ADC output "1" is present. And measuring-signal level grows until it exceed current level of the input analog signal.
It cause switching output signal to "0". And measuring signal begin to reduce level.

When the measuring signal level is lesser input signal of the ADC, its output is switched to "1". And measuring signal grows until the exceeding of input signal.

Read how to sigma-delta modulator works...

 

Such explanation causes difficulties in understanding what is actual difference between PCM and DSD and how to process DSD. Probably, it create myth about "native" DSD processing. About the processing read below in "DSD editing software" part.

Instead the explanation, in the author opinion, the easiest way to understand how to DSD works and process it is its spectrum considering.

To estimate DSD and PCM sound quality, the quantization-noise level is main criteria.

There is an explanation, that DSD has super high sample rate and, thus, super low bit depth 1-bit does not matter for noise.

But DSD 64 sampling rate (2,8 MHz = 44.1 kHz * 64), it is not enough to be better CD audio (see details).

To decrease noise level, noise shaping is used.

1-bit quantization-error (noise) energy have a significant level.

However, there is, so-called noise shaping of the spectrum is used. And quantization-error energy is re-distributed.

 

Noise shaping (NS) of 1-bit signal (spectrum)

Noise shaping of 1-bit signal

 

The quantization-noise spectrum (at the left of the picture) has level comparable with a musical signal. Sigma-delta modulator pushes significant part of the energy from low to high-frequency range, out of audible band (0 ... 20 kHz).

Noise shaping is implemented in sigma-delta modulator (a.k.a. DSD modulator).

When the 1-bit record is played back, low-frequency filter into sigma-delta demodulator (a.k.a. DSD demodulator, DSD decoder) cut the noise.

 

DSD decoder (demodulator)

DSD decoder

 

Therefore, at spectrum error level into the audible range is comparable with multibit pulse code modulation's (PCM) one.

Also, sigma-delta modulation may have multibit resolution. Read details below and watch the video at this page.

 

 

Sample rates

The format 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 no technical limitations for the sample rate value. But hardware/software compatibility issues are very probable.

 

DSD and Nyquist Theorem

For Nyquist theorem no difference between DSD and PCM: spectrum above [sample rate]/2 is the same to the spectrum below [sample rate]/2 and flipped along frequency axis.


 

Noise, Maximal Level and Stability Issues

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

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

To solve these issues the engineers have:

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

 

These parameters should be considered comprehensively.

 

Bit depth

Bit depth reduces quantization error level as itself.

 

Noise shaping

NS "push" significant part of the quantization error energy out of audible range.

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

Steeper NS can cause a higher probability of glitch (broken stability) of a sigma-delta modulator when input overload happens.
After the glitch, silence or some oscillations are generated at the output of sigma-delta modulator.
After broken stability, the modulator should be forcibly reset.

Overload tolerance of sigma-delta modulator

Overload tolerance of sigma-delta modulator

 

Sample rate

Higher sample rate reduces error spectrum level due distribution of its energy into a wider band. Also, it gives the ability to use sloper NS.

Energy is square of the figure, concluded between spectrum line and horizontal axis into band 0 ... [sample rate]/2.

 

Sample rate and quantization-error-spectrum level

Sample rate and quantization noise level

 

At the left and right pictures, squares of the noise energy figures are same. But figure, that more expanded in the horizontal axis, give lesser noise level.

Higher sample rate allows reducing the noise level in audible frequency range. It allows reducing noise shaping steepness, that increase overload tolerance of the modulator.

 

Resume

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

As an example, better quality is noise shaping implementation matter for the same bit depth and sample rate. But, on the other hand, we can increase the sample rate and/or bit depth to decrease error level for the same NS method.

 

 

DSD in figures

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

  • D64 about -125 ... -145 dB (comparable with PCM 24 bit)
  • D128 about -165 dB (better than pulse code modulation 24 bit)
  • D256 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 the noise should be maximally suppressed out of the band. Ultrasound noise can cause audible intermodulations distortions.

 

Read more about DSD vs DSF vs DFF >

 

DSD myths

Myth 1. DSD is better PCM and vice versa

No. Both format quality is defined by implementation in a device and software.

Also played back record is matter.

 

Myth 2. DSD has low noise level due to high sample rate

DSD's low noise level is a result of noise shaping.

 

Myth 3. Multi-bit DSD may be edited natively

DSD bit depth define noise level abilities. After DSD editing sigma-delta remodulation is need.

 

Myth 4. DSD editing with decimation dramatically degrade sound

The editing with decimation is implemented with low-frequency filter. The filter cause ringing audio.

However, no serious researches, that author know, studied the real impact of ringing to ears.

Also, the ringing depends on filter implementation.

So, currently, we don't know the exact answer to the question.

 

 

DSD vs FLAC, WAV, PCM comparison

Watch and share: DSD versus FLAC comparison
 

 

What is DSD? Quick explanation

What is DSD? Quick explanation

 

Bit depth define audible noise. More bit depth is lesser noise.

At the picture, we can see that bit depth decreasing achieved through using only part of the full signal frequency band. Other words, if we want to reduce bit depth, we must increase the sample rate to keep the audible noise level.

Read details of the format comparison in the table: DSD vs WAV vs PCM vs FLAC vs DXD

Feature DSD FLAC WAV PCM DXD
Coding sigma-delta modulation pulse code modulation pulse code modulation pulse code modulation pulse code modulation
Sample rate 44100 x 64 x N up to 384'000 Hz up to 2'147'483'648 Hz no limit 352 / 705 kHz
Bit depth

1 bit,
sometimes multibit

16 ... 24 bit,
32 bit some applications
integer only

16 ... 64 bit integer,
32/64 float point

multibit 24/32 bit
Band for audio signal Low part of the band Full band Full band Full band Low part of the band
Medium file, optical disk: SACD file file file, digital tape, optical disk: CD, DVD  

Note: WAV and FLAC are PCM implementations.

Read which is better DSD or FLAC (Infographic) >

Read more about audio file formats >

Direct Stream Digital (sigma-delta modulation) is like to pulse code modulation, but quantization error spectrum is shaped for decreasing noise into the audible range.

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

 

DSD versus PCM

DSD vs. PCM

 

PCM have lesser band reserve (above audible range) than sigma-delta modulation format, but pulse code modulation has higher bit depth.

Noise shaping for pulse-code modulation is implementation matter too, like sigma-delta modulation.

Therefore, no format advantages as itself. But implementation makes a difference.

Sigma-delta-modulation decoder (demodulator) is 2-position (1 / -1) voltage generator and low frequency filter. It is simpler than pulse-code-modulation hardware demodulator. Because pulse-code demodulator contains multi-voltage matrix or 1-bit decoder(s). So we have more abilities to make cheaper 1-bit DAC better than multibit one.

 

Read details here >

Also, look to infographic DSD versus FLAC >



 

 

PCM versus DSD ADC

PCM vs DSD analog-to-digital converter

PCM vs DSD ADC

 

Both kinds of DAC contains sigma-delta modulator. It converts the analog voltage to digital samples in a format like to DSD.

Before modulator analog filter ["DSD" sample rate]/2 is applied. Looks details here >

PCM ADC is more sophisticated and contains multibit modulator.

To reduce sample rate "multibit-DSD" signal should be filtered (low-frequency filter) and decimated (removing part of samples). The filter also eliminates shaped noise of "DSD signal".

Read more about PCM and DSD difference >

 

 

PCM versus DSD DAC

PCM vs DSD digital-to-analog converter

PCM vs DSD DAC

 

To easier providing of PCM DAC precision/linearity into this kind of DAC, a digital sigma-delta modulator is used. After it, sigma-delta de-modulator convert digital "DSD" to an analog signal.

In the general case, DSD DAC is simpler. It contains sigma-delta de-modulator only.

It is technically impossible to compare PCM and DSD DACs, because they use different processing / electrical circuits.

Read more what is DSD and PCM DACs and their comparison >

 

 

DSD vs PCM sound quality

There is no univocal answer. There is several reasons:

  • Quality of a record
  • Mixing/re-mixing of the record (including quality of the processing)
  • Playback software/hardware implementation
  • DAC implementation.

These reasons trigger infinite discussions "what is better PCM or DSD".

Technically, DSD and PCM are incomparable. Even as single DSD/PCM compatible DAC is used for the test, the difference may be caused by different mixing/post-production of records, and the DAC uses the different circuits (see here).

General answer: "Each case is individual and depend on playback system implementation and listened to record".

 

DSD sound quality and other [Brief F.A.Q.]

  • Are DSD downloads worth it? Are DSD files better?
        There is no unambiguous answer to the question. It depends on record quality, your software and equipment.
     
  • How big are dsd files?
        1 minute of DSD64 stereo is about 40 Mbytes.
     
  • Are all SACD DSD?
        Yes. Hybrid SACD also may contain CD layer compatible with usual CD player.
     
  • What are DSD music files?
        .dsf, .dff, .iso (sacd iso), flac/wav (DoP). Read details >
     
  • Why is DSD sounds better than PCM?
        Sound is defined by record quality, your playback program and apparatus.
     
  • Why upsample to DSD?
        Upsampling can optimize audio file resolution to optimal (minimal playback distortions) for your equipment. Read details >
     
  • Where to buy dsd music downloads?
        Read DSD store site list here >
     
  • Where to download dsd music free?
        Look at free DSD music download links >

Also read: DSD player F.A.Q., DSD converter F.A.Q., Myths

 

Is native DSD editing possible?

DSD editing is cutting, merging, gain altering, equalizing, etc. of file(s).

"Native editing" (without conversion to multibit and DSD re-modulation) is possible for cutting and merging DSD records only.

All other kinds of editing demand conversion to multi-bit values and re-modulation. In this case, loses of the editing in itself, comparable with PCM resampling.

Read details here >

 

 

File formats and compression method

  1. Sigma-delta modulation is applied on optical disks SACD (Super Audio CD).
  2. The modulation 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. Lossless 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 an open protocol that allows pack 1-bit audio as multibit for compatibility with software and hardware [4]. DoP cannot be played as usual pulse-code modulation.

 

Also, 1-bit audio may be streamed via a network.

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

 

Direct Stream Digital sources

DSD sources, mediums

 

Also, index file CUE + DSF/DFF audio files may contain 1-bit album.

Look at "DSD files" infographic >



 

How to play DSD?

DSD may be played at a mobile phone, portable players, music servers, SACD-players and other devices.

Some device can support native DSD feed of DSD DACs. Other ones demand pre-conversion to PCM or make conversion "on fly".

Sound quality is a complex matter. Read details about the resolution of audio files and sound quality.

Read details how to open, play DSD on Mac, Windows, iOS, Android, Linux: player list >

Read how to download DSD music and how to get free DSD files here >

 

DSD audio players (hardware and software) can playback all or some of the 1-bit file formats.

1-bit files may be played back directly on DSD DAC/player or converted to PCM "on fly" to playback to PCM DAC/player. About SACD conversion read more here

1-bit playback may be performed via special ASIO-driver under Windows, including DoP (DSD over PCM) digital audio packing format (example).

SACD optical disks may be played back at hardware player. Author knows nothing about available SACD-drives for consumer computers to playback/record SACD optical disks.

A stereo player may downmix multichannel to stereo. As alternative multichannel files may be pre-converted to stereo. It allows saving space on the hard disk of an audio player. Downmix is lossy audio processing. Its quality defined by an implementation.

Read more about the players here > and here >

Read DSD player software list >

 

DSD player brief F.A.Q.

  • Can iTunes play DSD files?
        Yes with additional software. Read details here
     
  • Can foobar2000 play DSD?
        Yes. Read details here
     
  • Can VLC play DSD files?
        As the author know, not. Details
     
  • Can Jriver play DSD files?
        Yes. Look at the player list
     
  • Can Vox play DSD?
        As the author know, Vox convert .dsf and .dff files to PCM on fly without native DSD playback.
     
  • Can Plex play DSD?
  •     As author know, Plex can playback DSF. Details
     
  • Can Musicbee play DSD?
        As the author know, yes. Details
     
  • Can Amarra play DSD?
        Yes
     
  • Can Audirvana play DSD?
        Yes
     
  • Can iPhone play DSD files?
        Yes. Look at the player list
     
  • Can iPod play DSD?
        As the author knows, there is conversion to PCM files is necessary.
     
  • Can Mac play DSD?
        Yes

Also read: DSD converter F.A.Q., DSD F.A.Q., Myths

 

 

How to convert DSD?

Read details how to convert DSD on Mac, Windows and other platforms: converter list >

How to create, edit DSD files read here >

How to rip DSD from SACD (to SACD ISO) read here

Watch and share: how to convert ISO to DSF, DFF
 

 

DSD converter is software that can perform (depend on implementation):

  • conversion DSD to PCM,
  • conversion PCM to DSD,
  • extracting SACD ISO to DSD,
  • extracting SACD ISO to PCM,
  • resampling 1-bit audio,
  • altering volume,
  • volume normalization,
  • click suppressing on track borders,
  • other processing.

Read how to works the converters here >

 

Converter list (convert some or all of DSD files [DSF, DFF, SACD ISO])


 

DSD converter brief F.A.Q.

  • How to convert to playback at iTunes?
        Convert DSF/DFF/SACD ISO to *m4a (ALAC, Apple Lossless). Read also (conversion DSF/DFF/SACD ISO to ALAC(m4a) is same) DSF to FLAC, DFF to FLAC, ISO to FLAC.
     
  • Conversion DSD to PCM degrade sound?
        Conversion with processing audio (including DSD to PCM) adds distortions. But final distortions is a matter of used playback distortions. Read details here
     
  • Conversion DSF to DFF and back is lossless?
        It may be lossless when audio converter doesn't process audio stuff (resampling and other) in conversion.
     
  • Do various DSD converters have different sound quality?
        Yes. There is noise level, frequency/phase distortions and tolerance to overload are estimated. Read details here.

Also read: DSD player F.A.Q., DSD F.A.Q., Myths

 

DSD editing software

Read main article about DSD editing >

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

Currently no information, that is known for the author, about "native" 1-bit processing (example: gain altering, resampling, etc.) without conversion 1-bit to multibit and back. Except, merging/dividing the audio file.

 

Read the article about DSD versus DSF versus DFF >

 

DSD editing

DSD editing

 

PCM here may be considered as "multibit DSD". Pulse code modulation is not obligatory to mean "24 bit / 352 kHz" or so on. Author recommends 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 need re-modulation with NS.

Losses of editing with 1-bit/multibit conversion are comparable with resampling.

Recording studios may distribute 1-bit 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.

Watch and share: Experiment with cutting ultrasound noise
 

 


 

 

What is DoP (DSD over PCM)?

DoP (DSD over PCM) is format to provide compatibility with some DSD hardware (USB DAC, for example). The format allows coding 1-bit DSD in usual multibit words (like PCM).

These multi-bit words are transferred as usual PCM. Upper bits of the multi-bit word contains special "DSD over PCM" marker code.

DoP receiver should recognize the marker code and interpret lower part of the multi-bit word as raw DSD bits.

DoP format may be stored into usual lossless PCM file: WAV, FLAC, AIFF.

DoP coding may be chosen in audio player settings.

 

DoP specification

 

 

 

DSD audio samples

Audio samples may be downloaded here:

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

Check more DSD downloading resources >

 


 

Conclusions

What Is DSD Audio? [Quick explanation]
  1. DSD (SACD) appear as improvement of CD-audio.
  2. Sound quality is not DSD/PCM format matter, but depend on implementation and quality of a musical record.
  3. "Native" DSD editing is possible for limited cases. For other cases, the own editing loses is comparable with PCM resampling.

Read the detailed article about DSD >

DSD is 1-bit audio data (sigma-delta modulation) format for hi-fi audio.

For the same sample rate and bit depth, the format may have different quality, that depends on implementation.

DSD digital-to-analog converter is simpler than the PCM one. It allows getting the better quality simpler way.

DSD may be edited via 1-bit to multibit and back conversion. The edition is lossy, except merging/dividing.

Read more about 1-bit format

  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? >

Author: ,
Audiophile Inventory's developer

June 02, 2020 updated  | since December 25, 2017

 


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