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Korg MR1000 & MR1

High-resolution DSD Master Recorders By Hugh Robjohns
Published March 2007

SOS were invited to take an exclusive first look at Korg's powerful new 1-bit high-resolution master recorders. It wasn't an invitation we could resist!

The ever-increasing capacity and falling price of solid-state Flash memory and compact hard disks has resulted in a glut of high-quality portable stereo recorders in recent years. The unique selling point for Korg's new offerings in this market, however, is that they support the Sony Direct Stream Digital (DSD) recording format (see 'The DSD Format' box), in addition to conventional and high-resolution PCM formats. Their MR1000 is a standard-sized recorder with a range of professional facilities, while the MR1 is an iPod-sized handheld device, based on the same technology, but with consumer-style interfacing.

Korg MR1000 & MR1

Core Specifications

The digital audio capabilities and operation of the two machines are almost identical. Both are stereo recorders that support a full range of linear PCM data modes, with sample rates from 44.1 to 192kHz. A 24-bit word length is standard, but 16-bit is an option for the base sample rates. The files are encoded in the WAV format, compatible with BWF (broadcast wave).

Both machines also support the 1-bit DSD format at the standard 2.8MHz sample rate. Three file formats are available, with the first being DFF — the standard DSD Interface Format File used for SACD production. The second is DSF, which is a DSD stream file format used in the audio software that comes with Sony's Vaio PCs. Finally, there is the generic WSD format (wideband single-bit data), which was created by the '1-bit Audio Consortium.' This is a group of manufacturers developing 1-bit consumer audio products, founded by Pioneer and Sharp and now including Accuphase, Clarion, Kenwood, Marantz, Sanyo, Sony, Teac, Toshiba, JVC and Yamaha, among many others.

The standard 2.8MHz DSD sample rate is 64x 44.1kHz, but it has long been argued that even this isn't really fast enough. Consequently, an alternative 128x rate is often used, at 5.6MHz. This mode is not included in the diminutive MR1 recorder, but is provided as an option in the MR1000, allowing Korg to market it as a 'resolution-independent master recorder', from which other formats can be derived at any point in the future, rather like storing digital camera images in RAW format for subsequent export as JPEGs.

Clearly, the high-resolution PCM and DSD formats require a lot of data storage. The 16/44.1 PCM format stores 90 minutes of audio per gigabyte, whereas 24/96 manages 25 minutes and 24/192 is only 13 minutes. In DSD mode, the 2.8MHz format gives 22 minutes of audio per gigabyte, while the 5.6MHz format in the MR1000 gives 11 minutes.

The larger MR1000 is fitted with a 40GB drive, which can store up to 60 hours at 16/44.1, while the tiny MR1 is equipped with a 20GB drive. The drives are formatted as FAT32, which can be accessed from a Mac or PC as an external drive via built-in USB 2.0 ports.

For both machines, the maximum continuous recording time is limited to six hours, but both can accommodate up to 200 tracks in each data format, and with up to 100 marker points in each track.

The backlit LCD screens of both machines are identical, with 106 x 108 pixels. The operating menus and displays are almost identical too (there are only a couple of very minor differences between the facilities of the two machines).

The MR1000

The larger of the two models measures 192 x 170 x 56mm and, despite its strong aluminium chassis, weighs exactly 1kg (without the eight AA batteries installed). It is supplied with a decent carrying case and shoulder strap, and a software CD (Windows XP and Mac OS X) with a program called Audiogate, which performs the file conversion as well as allowing some basic editing. A 56-page manual is also included, which is quite readable and well presented, although I found the machine so intuitive I barely had to look at the manual.

If required, the octet of AA batteries is inserted under a flap on the top panel. Alkaline or NiMH batteries are recommended, although the battery-level meter seems to be rather optimistic when it comes to NiMH operating life. The manual claims four hours of continuous operation on a set of batteries, and I certainly managed that easily on a set of high-power alkalines.

The rear panel carries a pair of combi-XLR sockets for the mic and line inputs, plus a pair of XLRs for balanced analogue outputs, and a pair of phono sockets for unbalanced outputs. The manual doesn't make this clear at all, but the TRS input is roughly 12dB less sensitive than the XLR input for a given gain setting, so line inputs should be via TRS plugs rather than XLR connections.

A square USB socket and a coaxial power socket are also on the rear, and a universal in-line 12V DC mains unit is supplied. Miniature slide switches select +48V phantom power and high or low input sensitivity, and activate a protective peak limiter. Using the input sensitivity switch, XLR and TRS inputs, and front-panel gain control, the recorder can accommodate signals from -60 to +26dBu — which should cater for most things! The balanced outputs operate at a nominal +4dBu with 0dBFS equating to +22dBU, while the unbalanced outputs are roughly 12dB lower in level.

The MR1000's front panel is neatly laid out, with intuitive, simple controls and a clear LCD display. The unit includes the impressive-sounding option of 5.6MHz 1-bit recording!The MR1000's front panel is neatly laid out, with intuitive, simple controls and a clear LCD display. The unit includes the impressive-sounding option of 5.6MHz 1-bit recording!Photo: Mike CameronIt is disppointing that there is no digital input facility, even if it only supported the PCM formats, as this would have added to the versatility of the unit. Likewise, the lack of digital replay outputs is a shame, although at least the files can be transferred to a DAW very easily.

The front panel is neat and simple, with a full-size headphone socket and associated volume control in the bottom-left corner. A dual-concentric record level control is stiff enough to avoid accidental level changes, but has no ganging mechanism between channels, so setting and maintaining an accurate balance is tricky, especially if you want to fade things up or down.

The transport controls are to the right of the LCD screen: forward and rewind, play/pause, stop, record, standby/on and Menu/Esc. These all have a positive action, with LEDs for play and record. An encoder wheel with an over-press switch is used to navigate the menu structure in a very intuitive way, with the Menu/Esc button exiting sub-menus. Three more LEDs indicate peak clipping for each channel, and warn of low battery.

The backlit monochrome display is very clear and readable, with the bulk of it being taken up by a horizontal stereo bar-graph meter (with adjustable peak-hold time). The song title and file format is displayed above the meter, with track time and transport status shown above that. When replaying tracks, a small bar shows the position through the track. Finally, an icon shows the status of external power or batteries.

Operating the MR1000 is extremely straightforward. To configure for a recording, you enter the 'record mode' menu to choose the file format and sample rate. After exiting the menus you simply press the record buttons to engage 'record ready,' set the levels, and then press play to start recording. Marker points can be added on the fly by pressing the record button (during record or playback) and edited within the library sub-menu.

All recordings are date and time stamped automatically, and files can be protected and renamed as necessary. The latter is reasonably quick and easy from a scrolling alphabet menu. Each recording is termed a Project, with two associated files: the audio file itself, and a Project settings file. The latter is only of relevance to the recorder and contains things like the protect status of the audio file and the marker list.

The protective limiter feature is not adjustable, other than switching it on or off, and there is no front-panel indication to show when it has been selected. In practice, it prevents overloads well enough, but it also has a pretty slow recovery time, which means that loud transients tend to 'punch holes' in the recorded track. I found it far better to work with a comfortable headroom margin instead (typically 12-18dB).

The built-in mic preamps are good enough, although I didn't feel that they lived up to the quality of the high-resolution recording formats on offer. Phantom power is within specifications and I had no trouble using a variety of capacitor mics, but I achieved noticeably better quality recordings by using a little Sound Devices MP2 two-channel battery preamp connected to the MR1000, using the balanced TRS inputs.

The line inputs produced clean and very low-noise recordings, as you would expect of a stereo master recorder, and I was generally pleased with the results. Using the mic preamps in the MR1000 alone, the input amp noise was undoubtedly audible, and for delicate and quiet acoustic musical performances I found it intruded more than I would have liked. Having said this, the unit's performance is on a par with its obvious rivals.

Connecting to the computer is simple. A standard USB 2.0 cable (not supplied) is connected and (with a PC) the USB slave mode enabled from the menu. At that point the unit is inoperative, but the drive is accessible from the computer as an external disk, allowing files to be copied as required. When connecting to a Mac, the unit has to be powered off before connecting, and on power-up it automatically enters the USB slave mode. Unlogging the drive from the computer and disconnecting restores normal operation.

Shutting the machine down takes a surprisingly long time. The Standby button has to be held down for a couple of seconds before a message appears saying it is shutting down... and that continues for 10 seconds or more, as the machine performs its hard drive housekeeping. Turning the unit on takes about five seconds, and retrieving a new file to play back takes a couple of seconds too. None of this is a problem, though it can all feel a little sluggish.

The DSD Format

Korg MR1000 & MR1Photo: Mike CameronAnalogue-to-digital conversion and back again: in concept, DSD is very simple and bypasses some of the filtering processes of traditional PCM conversion. However, there are complications: as the chart shows, a lot of high-frequency information is inherent in DSD recording and devices such as the Korg MR series have to be designed to filter this out.Analogue-to-digital conversion and back again: in concept, DSD is very simple and bypasses some of the filtering processes of traditional PCM conversion. However, there are complications: as the chart shows, a lot of high-frequency information is inherent in DSD recording and devices such as the Korg MR series have to be designed to filter this out.Photo: Mike CameronThe critical aspect of any digital audio system is the conversion to and from the analogue domain. Modern converters are all based on delta-sigma technology. A-D converters comprise a simple analogue low-pass filter, followed by a delta-sigma converter and a decimation filter to produce the required PCM output. D-A converters all use an oversampling filter, followed by a delta-sigma modulator and simple analogue low-pass filter.

The delta-sigma converter samples the audio with an extremely high sample rate but, because the signal voltage can't change much between samples, it only needs a very short word length to measure the difference — often only three or four bits, and sometimes only one bit. The decimation filtering stage then effectively trades the high sample-rate, low word-length data for lower sample-rate but long word-length PCM data.

However, the filtering has to have incredibly steep slopes to prevent aliasing, and that tends to leave a sonic footprint on the audio. Higher sample rates alleviate the problem, but don't resolve it completely, and what's worse is the need to filter twice: once in the A-D decimation filtering, and once in the D-A oversampling filtering.

The DSD approach avoids all that decimation and oversampling filtering completely. Instead of converting the signal to PCM for storage, it simply stores the raw high-sample-rate 1-bit output from the delta-sigma converter. On replay, that high-sample-rate data is passed straight to the simple analogue output filter. It is simple, cheap, and makes a lot of sense.

However, there are some down sides. The first is that delta-sigma A-D converters generate a huge amount of ultra-high-frequency noise, as the graph shows, and this can cause problems with analogue equipment in some circumstances. The other major problem is that performing signal processing — EQ, dynamics and so on — on a 1-bit DSD data stream is far from trivial. It can be done, but it is complicated, and there can be audible artifacts. In fact, there are only a few very high-end DAWs capable of working natively with DSD signals and, in practice, most DSD post-production is performed after converting the DSD data to high-sample-rate PCM!

The MR1 Handheld Recorder

This pocket version of the recorder is obviously aimed at the iPod generation! It measures just 64 x 120 x 24mm and weighs 200g, with chromed side panels and a silver grey-front: very stylish indeed. It's supplied with a sturdy protective case, a USB 2.0 cable, a miniature stereo electret mic and mounting bracket, and the Audiogate utility software.

The backlit display is the same as that on the MR1000, and the only front-panel controls are small buttons for record, play/pause, stop, forward and rewind. The headphone volume, on-off switch, Menu/Esc and encoder wheel have all been moved to the right-hand side panel, where they are easily controlled with a thumb. The on-off switch also has a 'hold' position to lock the controls against accidental operation, and the encoder wheel is now a thumb roller, but still with an over-press switch function. The headphone volume is set with separate up/down buttons.

The left-hand panel carries a coaxial 5V DC power inlet (a universal in-line power supply/charger is provided), and a miniature USB socket. The MR1 has a fixed internal lithium ion battery which is recharged when the external power unit is attached. Battery life is in excess of two hours of continuous operation, dependent slightly on file formats and backlight use.

The stylish MR1 is tiny, yet it accommodates a 20GB drive and is capable of up to 24-bit/192KHz PCM, as well as 2.8MHz 1-bit recording.The stylish MR1 is tiny, yet it accommodates a 20GB drive and is capable of up to 24-bit/192KHz PCM, as well as 2.8MHz 1-bit recording.Photo: Mike Cameron

The audio connections are on the top panel and are all 3.5mm mini-jacks. Two slide switches here activate 'plug-in power' (1.5V for electret mics) and switch between mic and line sensitivity. One mini-jack socket provides the stereo headphone output, while another provides a stereo line out with a nominal level of -6dBV.

The other two mini-jack sockets are for the left and right inputs and, unusually, these can accept either balanced or unbalanced sources. Miniature TRS plugs are needed for balanced inputs, and TS plugs for unbalanced ones or those requiring plug-in power.

While the provision for balanced inputs is useful, it also precludes the use of many commercial stereo electret mics (which are usually equipped with a stereo mini-jack plug), unless you have a suitable splitter lead. The specs suggest the maximum line input level is +6dBV and -27dBV for mics.

The recording level is set via an additional 'Rec Level' menu page, which allows each channel's gain to be set independently between -95.5 and +31.5dB — again, frustratingly, there is no ganged mode to set the levels of both channels at once. Alternatively, there is an auto-gain function which is effectively configured as a double-action compressor. If the signal level exceeds an adjustable threshold, the gain is reduced at a rate controlled by a 'Slope' parameter (attack), and when it falls below a second, separate threshold, the gain is increased at a rate determined by a second Slope parameter, but only if the level remains below that threshold for the Hold time value. It probably sounds more complicated than it really is, but it can be adjusted to work effectively and with reasonable subtlety, although it is better suited to speech recording than dynamic music.

Another interesting variation from the MR1000 is the provision of several DSD output filters. The larger machine simply has a filter on/off mode in the System menu. This rolls off at 18dB/octave above 50kHz to help reduce the very high level of ultrasonic noise that is present in all DSD signals, and which may cause intermodulation problems with some analogue amplifiers. However, the smaller MR1 unit has three filter options, the first being the same as the MR1000's. The others have steeper slopes and higher turnover points.

Pretty much everything else about the MR1 is the same as the MR1000 except, of course, that it doesn't support the double-rate DSD format, and the internal hard drive is 20GB instead of 40GB.

Obviously, the MR1 isn't capable of handling phantom-powered mics, so I used my Sound Devices preamp again to feed it with balanced line-level signals. With clipping at +6dBV (+8dBu), headroom was a bit of an issue in this configuration, but was resolved with in-line attenuators. I strongly recommend the use of right-angled mini-jacks with this kind of equipment, because the weight of the cables will cause the plug to rotate, rather than strain the socket's spring contacts, as would happen with straight connectors. Right-angled plugs are also less likely to pull out accidentally.

With balanced line sources the recording quality was very good (especially given the size and cost of the unit) and not noticeably dissimilar from the MR1000. I also recorded some interviews using the supplied stereo mic, and, although this was mechanically noisy if not handled carefully, it produced clear audio tracks with spacious stereo images.

High-resolution Mastering

Both the MR1 and MR1000 are well-designed recorders that are capable of high-quality, high-resolution results, but it is the double-rate DSD option of the MR1000 that will interest studio owners the most. There is currently no universally accepted format for storing stereo master recordings without having to make a sample rate and bit-depth decision at mixdown (unless you still count half-inch analogue tape at 30ips!). Korg's MR1000 allows you the luxury of capturing your analogue mixdown at the highest resolution currently available, for export in the format of your choice without compromising fidelity during conversion. The MR1000's £899 price point might seem like a lot when most of us can so easily master back to our DAWs, but the real comparison should probably be with a high-quality half-inch analogue recorder. Then the MR1000 starts to look like a real bargain! 

Alternatives

The Fostex FR2 and Tascam HDP2 machines occupy slightly more professional territory than the MR1000, thanks to their timecode facilities, but they lack the DSD formats, so perhaps the Marantz PMD670 is a fairer benchmark. The MR1 competes more squarely with devices like the Edirol R09 and M-Audio Microtrack, along with devices from Nagra and others, although the DSD feature and balanced inputs help to give it an edge.

Pros

  • Very high sample-rate PCM and DSD formats.
  • Audiogate software allows exporting into other formats.
  • Very intuitive user interface.
  • USB 2.0 file transfer.
  • Robust and reliable.
  • MR1000 has phantom power and balanced I/O.

Cons

  • No digital I/O
  • Preamps very good, but no match for the recording format potential.
  • Battery life.
  • Unganged record level controls.

Summary

Hard disk recorders with identical core functionality, but different physical formats. Supporting 1-bit as well as conventional PCM recording formats, and very high sample rates, both units are capable of good-quality recordings, in an easy to use, fuss-free operating environment.

information

MR1 £499; MR1000 £899. Prices include VAT.

Korg UK Brochure Line +44 (0)1908 857150.

+44 (0)1908 857199.

info@korg.co.uk

www.korg.co.uk

www.korg.co.jp

Published March 2007