I. General Technical Background
The Digital-to-Analogue converter (D/A converter or DAC) converts digital (discrete) signals (normally: a time series of binary numbers) into analogue (continuous) signals (normally: a stream of voltages). It is of crucial importance for the quality of digital music playback. Just like the A/D converter largely determines the quality of the modulated digital signal, so the D/A converter determines how faithfully this signal gets converted back to the original analogue signal. There are quite a number of alternative technical methods for realising these conversions. In audio applications the two most important ones are: Delta/Sigma DACs and R-2R Ladder DACs. More recently, there is also a NOS-DAC concept (NOS= Non Over Sampling), which is usually a special variant of the Ladder-DAC concept.
At the beginning of the digital era, most audio DACs were of the R-2R type. A R-2R Ladder DAC is a binary-weighted DAC that uses a repeating cascaded network of resistors of values R and 2R, connected to a summing point, typically an operational amplifier. The network can be discreetly built up of individual resistors or integrated in ICs (like in the famous Philips TDA1541/TDA1543). The bit inputs Bit0 to Bitn-1 are switched between ground (V=0) and the reference voltage (V=Vref). The R–2R network causes these digital bits to be weighted in their contribution to the output voltage Vout. Depending on which bits are set to 1 and which to 0, the output voltage (Vout) will have a corresponding stepped value between 0 and Vref minus the value of the minimal step, corresponding to bit 0.
This converter technology excels through high speeds, high bandwidth as well as excellent signal to noise ratios. However, this technology did not prevail. Today ca. 95% of DACs in audio applications are of the Delta/Sigma type. The reason for this is not its undoubted quality, but its relatively high cost. The R–2R ladder operates as a string of current dividers, whose output accuracy is solely dependent on how well each resistor is matched to the others. The required accuracy doubles with each additional bit. At 16 or even 24 bit, the required accuracy is extremely high and costs of such resistors correspondingly steep. Nonetheless, many highend audio companies, like MSB Technology, dCS, 47Labs, Zanden, Audio Note and DAS use DACs with R-2R ladder technology.
You can read more about digital conversion technology in our background article: D/A Converter Technologies.
Whether upsampling improves sound quality is controversial. Many audiophiles believe that upsampling improves high frequency sound reproduction and with it spatial representation.
Technically speaking, upsampling does not change the resolution of the musical data. Upsampling merely:
- interpolates identical sampling data: the sampled data are copied and the corresponding number of copies (1x or 3x) gets inserted after the last original sample and in front of the next original sample. Thereby the existing samples are doubled or quadrupled, without any change in the underlying sampled data.
- interpolates zeros below the previous LSBit: in a 16bit file, upsampling inserts 8 zeros below the previous LSBit, increasing the bit depth to 24bit without adding any further information; in 24bit files nothing happens.
The reason, why this may lead to an improvement in the quality of music reproduction lies in the converter technology used, rather than in the music files. The most widely used conversion technology nowadays is delta sigma, which relies on digital brickwall filtering to reconstruct the analogue signal. Brickwall filtering causes various unwanted side effects, like phase shift, distortion, pre-ringing etc. In such converters, increasing the sample rate (even without adding any new information) may improve sound reproduction by moving the application point of the brickwall filter away from the audible spectrum (20-20,000 Hz). E.g., in a CD standard file of 44.1kHz/16bit the brickwall filter will cut off the signal sharply at 22.05kHz, causing phase shift, distortion, pre-ringing etc. well into the audible spectrum. With Upsampling the brickwall filter’s application point gets pushed out to 44.1kHz or 88.2kHz, so that the audible spectrum is less affected.
In converters without brickwall filtering, upsampling will most probably make no difference.
Upsampling across sample rate families (44.1, 88.2, 176.4 and 352.8 kHz on the one side and 48.0, 96.0, 192.0 and 384.0 on the other) should be avoided, because otherwise interpolation may lead to uneven fractions increasing the calculation load on the CPU. Although this was more of a problem a few years back, when CPUs were not as powerful as they are today.
Assuming, they work without error, there are basically 2 areas where data drives can have an influence on sound quality:
- The noise of the drive or resultant vibrations could be annoying, at least in quiet music passages. Here SSDs have a fundamental advantage, since they work entirely without any moving parts. On the other hand, you can install HDDs so that they are similarly quiet. DAS installs its HDDs in blocks milled from solid aluminium in order to isolate the HDDs acoustically and thermally. Consequently, SSDs offer no real “quietness” advantage.
- Reading speed of the drives could be too low for music files with high data rates (high resolution music files), resulting in skips during playback. However, the speed of modern HDDs – while not as high as that of SSDs – is still more than sufficient for audio applications, even at extrem resolutions, so that SSDs offer no speed advantage.
Independently of sound quality, SSDs do have the advantage of generating less heat and therefore putting less thermal burden on the overall system.
Summing up, we see no compelling advantage for the use of SSDs compared to high quality HDDs in audio players. Given the substantially higher prices for SSDs, we do not particularly recommend their use. Consequently, as standard, we install high quality HDDs for data storage. But on customer’s request (and at additional costs), we are also happy to install SSDs. Just to clarify: this applies to data storage drives. For operating system and application software, DAS uses a separate SSD.
The question about the qualitative influence of MQA encoding is controversial. To do justice to that question, we have to cover a wider ground:
- There are 3 types of audio encoding:
- Uncompressed and lossless codes (e.g. WAV)
- Compressed and lossless codes (e.g. FLAC)
- Compressed and lossy codes (e.g. MP3)
- MQA is a hierarchical, compressed and lossy codec (type 3.) incl. a kind of copy protection, developed by Meridian Audio Ltd. and now owned and licensed by MQA Ltd. MQA encodes music files through adaptive differential pulse code modulation (ADPCM) and bit rate reduction.
- An MQA data stream is decoded hierarchically: in MQA licensed devices, depending on the type of license, in partial resolution (“1. Unfold” with software decoder) or full resolution (“2. & 3. Unfold” with hardware decoder). In non-MQA-licensed devices, the data stream will be decoded up to effectively 13bits only. Even in MQA licensed devices at 1. Unfold only up to effectively 17bits. The remaining bits are reserved for various “foldings” (see patent description here). The patent description is not particularly transparent (there is a “touchup” function - however that works) and the people behind MQA have done little to clarify the exact workings of their codec. However, MQA effectively causes data loss and reduces dynamic range. Additionally, various analyses suggest, that the MQA coding/decoding adds substantial distortion and noise to the resulting analogue signal (Archimago, XiVero, Golden Sound).
- In Hi-Fidelity we normally prefer lossless codecs. Lossy codecs do have a role to play, particularly in applications where there is bandwidth limitation, like in mobile uses. In your home stereo there is normally no such limitation, so that there is no advantage of using a lossy compression.
- The reasons why MQA is nonetheless intensely discussed in Hifi circles has to do with the marketing promises by MQA Ltd. and the different interests of the parties involved:
- Massive advertising by MQA Ltd. with the - at least partially - misleading claims that MQA:
- can deliver highres content at CD standard data rates, i.e. can substantially reduce bandwidth requirements
- is Lossless
- improves the sound of a given file by various means, inter alia by correcting the damages caused by digital filtering (pre-ringing) in the A/D converters used in production (“white glove treatment”)
- has an MQA authentication procedure, ensuring that the user hears exactly what the artists and engineers approved of as the definitive version of the title.
The HiFi press was enthusiastic at first. E.g., Robert Harley, editor of The Absolute Sound has referred to it as "The most significant audio technology of my lifetime". Only later on did it turn out that:
- the claim to reduction of bandwidth requirement seems not to be tenable: Analyses of Archimago and Golden Sound suggest, that in CD standard, file size is slightly larger than normal despite reduced bit depth; in highres files data rates correspond to PCM data rates in FLAC format for the reduced bit depth
- the claim to “losslessness” is untrue and in any way in contradiction to MQA’s own AES paper presentation of Oct. 2014
- How the ex-post filter corrections are supposed to work is a mystery. In any modern recording session, there are numerous A/D converters involved for any one album, most of which never get recorded.
- Various reports of artists on Tidal (e.g., N. Young, Golden Sound, FredericV.), suggest, that the MQA files for which the MQA authentication is provided, do not represent, the files submitted by them. In fact FredericV showed that he could remove 30% of the data in his files and they would still be shown as “authenticated”.
- For the record industry, MQA is yet another argument to resell their old archives (I am sometimes smiling at myself for having bought the same album up to 7 times in search of the best sounding version: 1. Original LP, 2. Half-speed mastered LP, 3. Digitally remastered LP, 4. CD, 5. Remastered CD, 6. SACD or DVD-A, 7. Highres download. With each new version, the record industry promised better sound quality. Sometimes that turned out to be true, sometimes not. This time they come up with MQA.)
- MQA offers the record industry a license test and thereby a method to contain the free exchange of music files
- MQA offers MQA Ltd. license fee income, a) in terms of hardware licenses, and b) in terms of music licenses even for albums, for which MQA is no rights holder
- For hardware manufacturers, MQA is an argument to sell their customers new hardware
- And finally, some albums do indeed sound better as MQA versions, after they have been newly remastered for MQA from highres source files. The improvement in sound quality is then, presumably, due to the new mastering rather than the encoding technology. Archimago has done a blind comparison of identically mastered highres MQA and PCM files with a pool of 83 audiophiles and musicians in 2017. Similarly, McGill University has conducted a double-blind ABX test, submitted to the AES in 2018. The result in both cases was that the test persons could not detect any difference in sound quality between the highres MQA and PCM files. However, most MQA albums available are simply MQA-coded CD-masters and sound like the old CDs, just with reduced dynamic range.
Summing up, MQA does not seem to offer an advantage to the music connoisseurs in the context of his or her home stereo. MQA may, under certain circumstances, offer advantages for music connoisseurs under circumstances of reduced data bandwidth. At its core, the MQA technology is a very complex process to show that one can generate music files by bit rate reduction from 24bit to 17bit that are not distinguishable by the human hearing. This could have been achieved a lot easier by bit rate reduction in PCM and FLAC with similar data file sizes – entirely without license fees and costs.
In the context of file based music playback, MQA is actually only relevant for subscribers of the TIDAL streaming service. That is TIDAL’s attempt to provide highres streaming with low data bandwidth. However, TIDAL with its so called “TIDAL Masters” (MQA coded highres files) is fairly intransparent with regard to the actual resolution of the files streamed. TIDAL offers no data about sample rate or bit depth. This is in contrast to Qobuz, which streams PCM data in FLAC format and provides detailed information about file resolution.
5. Are there Differences in Sound Quality between WAV and FLAC File Formats? Which one is better for CD-Ripping?
There are no differences in sound quality between WAV and FLAC file formats. The best file format for CD ripping is the FLAC format, for 4 reasons:
- It is universal and there is hardly a player that cannot handle it
- There is no sonic difference to uncompressed formats like WAV
- Compared to WAV, FLAC requires only about half of the storage capacity (depending on compression level)
- In contrast to WAV, FLAC has implemented the tag standard Vorbis comment, so that it is a lot better and easier to manage file tags with FLAC than with WAV
FLAC is a lossless file compression format. This means that no data are lost in compression or decompression (otherwise it would not be lossless). Consequently, WAV can have no sonic advantages. 20 years ago there was this aspect that the real time decompression of FLAC files during playback could put a heavy load on the comparatively weak CPUs of the time, so that there was a higher probability for skips and distortion. If ever it was a problem, it is certainly no issue with contemporary computers that have more than sufficient CPU capacity. Today there is no advantage of using WAV files, but there is the disadvantage of big file sizes and tagging problems.
Server and streamer are different sources for digital music playback:
- A server delivers music from a local storage that you have previously purchased (Download) and to which you have unrestricted access at any time
- A streamer delivers music from a remote storage that you do not own, but to which you have purchased a temporary right of use (Subscription). If you want to listen to the same piece of music again next month, you will have to pay for it again (subscription fee next month). If your subscription expires, your music is gone. If your streaming provider goes bankrupt (which is not unlikely, given the economic condition of most streaming providers), your music is gone. If your internet connection fails, your music is gone (at least temporarily). In return, streaming offers an enormous choice.
In our view, it is most likely that both sources of digital music - download and streaming - will exist side by side for some time in the future. The combination of both allows consumers to discover new music with streaming services and to purchase and own the pearls of their new discoveries in top quality per download. The situation is similar to the last 80 years of consumer electronics, where the radio (and later the tuner) had its place besides the record player (and later the CD player) in consumers’ living rooms. They listened to the radio in the background. And of all the radio music they heard, perhaps 1% they thought of as interesting. And for those 1% they went into a record store and bought the appropriate album. Similarly today with streaming and downloads: the music connoisseur appreciates both: a platform with enormous choice to savour and discover new music (Streaming) and a platform to purchase and own selected pieces of music, that are close to his or her heart, at the best available quality (Download).
II. DAS HD-Player
In our experience, good analogue music playback (reel-to-reel, vinyl) sounds – ceteris paribus – livelier, more realistic and more emotionally engaging than even high quality digital playback. This is actually puzzling when you consider that in all measurable parameters, digital music playback is vastly superior to analogue playback. It has been our ambition from the start to realise in the digital domain the atmosphere and vivid realism of high-end analogue equipment and to combine that with the convenience of digital music management. According to independent test reviews, we have fully achieved that goal.
Of course, we haven’t achieved that by transferring the limitations of analogue music reproduction to the digital domain. But we achieved it by combining all the benefits of digital music reproduction (linear frequency response, higher dynamic range, lower distortion, phase linearity etc.) with the advantages of analogue reproduction, by delivering the same liveliness and realism that you are used to from analogue sources – just with less noise, more dynamic range and more spacial openness. That is technically feasible, but complex.
DAS utilizes a special D/A conversion topology, called NOS R-2R ladder DAC, which do not require any oversampling or digital filtering.
Oversampling and digital filtering are the main reasons for the so called „digital sound“, i.e. a sound quality that is clear, transparent and dynamic, but at the same time also flat, glassy and unengaging. In audio applications ca. 95% of all D/A converters used today are of the oversampling type. Oversampling D/A converters up-sample all incoming digital signals to a multiple of the original sample rate in order to reduce the anti-aliasing filter requirements. These oversampling chips are so popular, not because they sound so good, but because they are cheap to purchase and easy to handle. Repeated up- and downsampling of the original signal with associated filtering is not conducive to good sound quality.
To build a D/A converter without oversampling is a lot more complicated and costly. But it leads to unadulterated and natural sound reproduction.
Modern delta sigma DACs mitigate the effects of digital filtering by offering the user a selection of various different reconstruction filter types, like “apodizing”, “minimum phase”, “linear phase”, “slow-roll-off” etc.. These filters can partially mitigate individual aspects of the side effects of digital filtering (like, aliasing distortion, phase distortion, bandwidth limitation, impulse response etc.), but only at the expense of other aspects. In other words, with these filters, the user can push around the damages of digital filtering, but can never get rid of them. Consequently – and that is true of all delta sigma converters – they will never be able to reproduce the original sound. Because the original simple did not contain any pre-ringing, bandwidth limitations or phase distortion. DAS HD-Players do not cause any such problems and therefore do not require any measures for their mitigation.
To learn more about digital converter technologies, you can read the technical background article: D/A Converter Technologies.
No. You do not require any further hard- or software components to fully utilize our HD-Players. Every HD-Player comes with an Apple iPad and all necessary software preinstalled and configured. Just unpack and start listening to glorious music.
Roon is not required for our HD-Players. Just like Roon we think that supplementing music albums with multi-media content is an important enrichment of the musical experience. In particular, we want to recreate some of the haptic quality of the vinyl era with its cover art and liner notes in the digital realm. In contrast to Roon, we achieve that not via a permanent online connection and yet another subscription, but locally. You can learn more about our user interface here.
Yes. DAS HD-Player stream MQA music from TIDAL with 1. Unfold (up to 88.2kHz, resp. 96.0kHz). For more details about the advantages and disadvantages of MQA encoding, see FAQ no. 3 of the general technical background section.
Yes. Our HD-Players offer the option to up-sample music files 2x or 4x to 176,4kHz or 192,0kHz. For more details about the advantages and disadvantages of up-sampling, see FAQ no. 1 of the general technical background section.
Up-sampling generally only helps the performance of delta sigma converters, given the problematic role of the unavoidable use of digital brickwall filters. Our HD-Players use a completely different converter technology, without any digital reconstruction filters. Consequently, they cause not damage to the reconstructed analogue signal and thus do not need any corrective measures. Generally: If you do not cause any damage, you do not need to implement repair mechanisms. Nonetheless, we have implemented up-sampling for 2 reasons:
- Surprisingly many people swear by up-sampling, quiet independently of its objective effects
- Our HD-Players offer digital outputs to connect to external DACs, for which up-sampling may have beneficial effects. These effects will be in proportion to the quality of the reconstruction filters of the external DACs – the better the filters, the less effect up-sampling will have.
As standard, we deliver our HD-Players with 4 TB of HDD data storage (sufficient for about 11.000 CDs in FLAC format). If you wish, we can also deliver our HD-Players with SSDs at additional costs. Given the additional price, we do not normally recommend it. Our standard HDDs are encapsulated in a solid block of milled aluminium for thermal and noise isolation. Our HDDs are almost as quiet as SSDs. So, there is no real noise advantage. The speed of HDDs is more than sufficient for audio playback, even at extreme resolutions. So, there is also no speed advantage.
To be clear: the operating system and application software of all HD-Players is stored on a separate SSD. Here we are only talking about music media data storage.
Maximum music data storage sizes:
- With HDDs you can have up to 6 TB
- With SSDs you can have up to 12 TB
There are 2 ways to transfer music files to the internal music storage of the HD-Players:
- If you are connected to your home network via LAN or WLAN, you can simply use the standard file manager of your computer (Finder, Explorer) to drag ‘n’ drop any media files from the hard drive of your computer or connected NAS to your HD-Player.
- Independently of whether you are connected to your home network, you can connect a USB drive (stick or external drive) to any of the USB sockets at the back of the HD-Player. The DAS software detects any media files automatically and intelligently synchronizes the media files o the USB drive with the media files in your internal music archive. It will copy only those files from the USB drive that are not already in the internal archive.
Yes. There is an easy-to-use backup functionality in the user interface of the HD-Players. The backup functionality operates incrementally, so that the first backup is a full backup. Any further backups only add the changes compared to the last backup, so that backup time is considerably reduced.
Although we only use the best hard drives available and thoroughly test every HD-Player before delivery to our customers, there is always a risk of hard drive failure. We therefore recommend regular backups of your valuable music collection.
You can connect your HD-Player to the internet via either LAN cable (Ethernet) or WLAN (WiFi).
Additionally, you can use your HD-Player entirely without router or network, if you prefer. If you do not connect your HD-Player to either a LAN or WLAN network, then the HD-Player connects itself automatically to your remote control tablet or smartphone via access point modus and can be operated stand alone.
In our experience the sound of our HD-Players will improve continuously during the first ca. 50 hours of operation. After that we could not notice any further changes in sound quality. We therefore recommend a break-in period of about 50h. Since our HD-Players have to pass a 24h test procedure before being shipped, any new owner should allow for ca. 26h of operation before seriously evaluating sound quality.
The main differences between the Model 2 and the Model 4 are:
- The Model 2 can be operated either through the displays and keys on its front or through a remote device like a tablet or smart phone. The Model 4 by contrast can only be operated through a tablet or smart phone.
- The Model 2 has a fully symmetrical design like studio equipment. This is ideal if you want to connect the Model 2 symmetrically to your other audio devices via XLR interconnects. Of course, the Model 2 also has unbalanced RCA outputs. The Model 4 has unbalanced RCA outputs only and has consequently a slightly lower dynamic range compared to the Model 2.
- The Model 2 has a complete dual mono layout, i.e. from the power supply throughout the entire signal processing until the analogue outputs, the two channels are completely separated. The Model 4 has a stereo layout, so that it has a slightly lower channel separation than the Model 2.
In total this results in the Model 2 having a bit more dynamic range, somewhat lower distortion and delivering a slightly larger spacial presentation of the musical material, compared to the Model 4. However, the Model 4 already performs on a very high level in all of these respects, as testified by independent reviews.
Yes. We will publish updates of our software from time to time to enhance the functional range of the HD-Player or to correct errors detected. We will inform our customers per email of the availability of any software updates.
We have purposefully not included the playback of internet radio in our HD-Players. The sound quality of our HD-Players is exceptionally high. Internet radio usually streams in mp3 format with data rates of between 64kbit/s and 192kbit/s, which is a fraction of the data rates delivered by streaming services. The low data rates of the internet radio are useful wherever available internet bandwidth is seriously limited, such as listening to music in the car or on a mobile phone. At home, where no such limitation exists, it makes no sense to compromise sound quality for data rate. Additionally, modern streaming services offer in excess of 60mn titles so that there is hardly a piece of music that cannot be found with one of the streaming services.