Ultimately, most electronic musicians want to record their music so it can be played and enjoyed (and hopefully bought!) by others. Most of us are familiar with analog tape, such as 1/4-inch reel-to-reel or cassette, which has been widely used for many years. These days, however, more and more musicians are recording their material digitally, which is fundamentally different from analog recording. (For the basics of digital audio, see "Square One: Digging into Digital Audio" in the February 1996 EM.)

Digital audio signals can be recorded to tape, hard disk, MiniDisc, or computer memory (RAM or ROM). For long musical parts (e.g., vocals, acoustic guitar parts), tape, MiniDisc, and hard disk are the preferred media because they can hold much more data than RAM or ROM, and they provide permanent but changeable storage.

DECISIONS, DECISIONS

Once you decide to digitally record your tracks, you must then decide whether to record to tape or hard disk. If you decide to use a hard-disk recorder (HDR), you must choose between a computer-based or modular system. For now, we’ll focus on hard-disk recording.

Computer-based HDRs (which are also called digital audio workstations or DAWs) require a PC, Macintosh, or other general-purpose computer and include a software package and perhaps a hardware interface to get audio into and out of the computer. These systems offer a large graphic display (the computer monitor) and, in some cases, integration with MIDI sequencing. Effects are sometimes incorporated into the basic software and often can be added in the form of DSP plug-ins (more on this in a moment). Of course, computers are relatively expensive, especially those with enough horsepower to handle hard-disk recording. Desktop computers are not easily portable, but modern laptops can often perform hard-disk recording, as well.

Modular hard-disk recorders (M-HDRs) are self-contained units with built-in hard disk, mixer, and, in many cases, effects. Their "brains" are nothing more than computers dedicated to hard-disk recording. In most cases, you can combine several M-HDRs as need requires and budget allows, and you can sometimes control multiple M-HDRs from a single control panel. This is similar to modular digital multitrack (MDM) tape decks.

M-HDRs are dedicated devices with familiar, tape deck—style controls. In addition, they are quite portable. However, they offer far fewer editing features than are available in most computer-based DAWs. M-HDRs have a relatively small display, which makes even basic editing more difficult than with a DAW. In addition, they require external synchronization to integrate with a MIDI sequencer. On the up side, M-HDRs are much more stable–crashes are far more common with computer-based systems–and because they have fewer in-depth editing features, they are generally easier to master.

STORAGE CAPACITY

Digital audio that is recorded at a sampling rate of 44.1 kHz with a resolution of sixteen bits requires about 88 KB per second per track or 5.3 MB per minute per track. As a result, a 3-minute song with eight tracks would consume 127 MB of space. I recommend that you use a hard drive with at least 1 GB for digital audio data.

Some HDR systems use data compression to reduce the storage requirements. Common forms of compression include µLaw (pronounced "myu-law"), Macintosh Audio Compression/Expansion (MACE), and Adaptive Differential Pulse Code Modulation (ADPCM). Some types of compression, including most of the types currently in use in audio systems, can degrade the sound quality. Lossless compression does nothing to the sound quality, but it yields the least amount of storage savings. Lossy compression actually removes some of the data, which can degrade the sound quality, but it yields greater savings, typically from 4:1 to 6:1 or more.

OTHER IMPORTANT CRITERIA

HDRs can use several types of hard-disk media (which I’ll cover shortly). However, they must all meet certain minimum criteria to be practical for this application. The most important of these criteria are average access time and throughput.

Access time (also called seek time) is the time it takes the drive to find a piece of data anywhere on the disk. Of course, if the disk drive’s read/write head is near the location of the desired data, it takes less time than if the head is far away from the data. As a result, the average access time is calculated and used as a benchmark.

Throughput (also called data transfer rate) is the amount of data that can be sent to and from the disk per second. You can record many tracks on most hard-disk systems, up to the capacity of the disk. However, you can only play a limited number of tracks simultaneously, depending in part on the processing speed of the computer and the average access time and throughput of the disk.

If you’re shopping for a hard-disk drive to use for digital audio recording, you might think it’s as easy as finding a drive that meets certain seek time and throughput specs. As a general rule, any hard disk used for digital audio recording must have an average seek time of 12 milliseconds (ms) or less and a sustained throughput of 3 to 4 MB per second (MB/s) or more. However, it’s actually a bit more complicated than that. For one thing, the minimum acceptable specs depend on the number of tracks the system must deal with simultaneously; an 8-track HDR requires a faster hard disk than a 2-track system.

In addition, many hard drives perform a routine called thermal recalibration, which compensates for slight changes in the size of the disk platter due to temperature variations. If this occurs during recording, you might miss several milliseconds of data. You can sometimes turn this function off or tell the drive to perform it only when it is not writing or reading data. Fortunately, many modern hard drives now use other means of compensation for temperature changes.

Finally, the type of connection between the computer’s central processing unit (CPU) and the hard disk affects how much data can be transferred to and from the disk in a given amount of time. Some of the more common types include SCSI, IDE, and ATA. In addition, each type of connection includes at least two variations, each with its own maximum throughput. For example, the original version of SCSI can deliver a theoretical maximum throughput of 5 MB/s, while the newer Fast SCSI-2 can sustain 10 MB/s. Then there’s Fast and Wide SCSI-2, which can sustain up to 20 MB/s. (For more on these hard-disk connections, see "The Windows Studio" in the July 1996 EM.)

Fortunately, you don’t typically need to worry about these issues. All you need to look for is an "A/V capable" drive, which should meet all minimum requirements for recording digital audio. In fact, most modern hard drives are A/V capable. Some computer-based DAWs, such as SADiE Inc.’s SADiE 3, supply a turnkey system, complete with suitable hard drive, while others, such as the various systems from Digidesign, provide a list of drives that have been tested for compatibility.

TYPES OF MEDIA

There are several types of hard-disk media, and most are available in external boxes or as internal units for computers or M-HDRs. The traditional type of hard disk is called a fixed disk, which is permanently sealed within an enclosure.

Removable cartridges behave much like floppy disks, but they hold much more data. Most of the older removable-cartridge drives are not fast enough for hard-disk recording, but recent advances in removable technology have enabled a few such products to be used for this purpose. Examples include the Iomega Jaz (1 GB) and SyQuest SyJet (1.4 GB) and SY270 (270 MB). Akai uses magneto-optical (MO) removable media in their 8-track DD1500 M-HDR. This requires a custom controller chip and some sophisticated buffering of the data because MO technology is otherwise too slow for hard-disk recording.

One of the most important advantages of removable media is the fact that you can easily store the audio for each project on a separate cartridge. This makes it easy to keep track of your data and lets you take the cartridge to other studios. Removable media are also great for backing up your data (more on this in a moment).

MiniDisc is a relatively new type of removable MO cartridge that is being used in low-cost M-HDRs from Yamaha, TASCAM, and Sony. These units resemble the ministudios of the past, except that they use MiniDisc cartridges instead of cassette tapes. They can record and play up to four tracks of audio (no virtual tracks are possible), and the storage capacity of a cartridge is 140 MB. These units use lossy 5:1 compression to record up to 37 minutes of audio per track. (You can also record in stereo for a total time of 74 minutes per track or in mono for a total time of 148 minutes.) According to the manufacturers, if you want to record four tracks, you must use MD Data cartridges, but for stereo recording, standard MD Audio cartridges work fine.

RECORDING AND PLAYBACK

Basically, recording on an HDR is similar to using a traditional analog tape deck. Most HDRs provide tape-style transport controls, such as Play, Record, Rewind, Fast Forward, and Pause. Unlike tape decks, however, HDRs take virtually no time at all to jump from any point in the music to any other point thanks to random access. This means that the hard disk can find any piece of data in roughly the same time as any other data. By contrast, tape is linear; it must be shuttled to find a particular spot in the music. You can also punch in and out, and this does not necessarily replace the material in the punch section.

Most HDRs let you record lots of tracks (though rarely more than eight at once), and you can typically play between two and eight tracks simultaneously from a single unit. Some systems (such as Digidesign’s Pro Tools III) allow expansion to sixteen tracks and more. Even though an HDR might be called an 8-track device, it can typically hold many more tracks of data. These are sometimes called virtual tracks, which let you record many takes of each part and select the best one for playback.

In most cases, random access, nondestructive punches, and virtual tracks are possible thanks to the use of pointers, which are internal indicators the computer uses to identify and manipulate different sections of the audio data. For example, let’s say you’ve recorded a guitar solo, and you punch into the middle of the solo to correct some mistakes. On tape, this would destroy the original material in the punch section.

With nondestructive editing on an HDR, however, the new material is stored on a different part of the disk, leaving the old material untouched. When the solo is played back, the computer uses pointers to jump to the new material and back to the old material at the correct moments. This lets you use either version of the punched section.

Pointers are also used to select the virtual tracks you want to play; you can even assemble material from several tracks into one composite track without destroying the original data. The user doesn’t work with pointers directly. Instead, you tell the HDR which parts of which tracks you want to use by creating a playlist (sometimes called an edit decision list, or EDL), which is a list of the audio sections you want to play back in a certain order.

Many studio operators need to sync the HDR with a MIDI sequencer and/ or tape deck. This is not a big issue if you are using a digital audio sequencer that integrates hard-disk recording and sequencing. If you are using separate programs to sequence and record to hard disk, internal synchronization usually works well but not always. There are different degrees of sync: some systems just trigger the audio files and MIDI files and hope they stay together, and other systems repeatedly check the synchronization and adjust the playback as required. Obviously, the more often the system checks its synchronization, the tighter the sync is likely to be.

Most M-HDRs include some form of synchronization capability, such as MIDI Time Code (MTC) or SMPTE. In some cases, these devices can only be the master time-code source, which means that the other devices in your system must sync to the HDR. In other cases, the HDR can be master or slave. If you are using a tape deck in conjunction with an HDR, the tape deck must be the master, so your HDR should be able to sync to it.

EDITING AND MIXING

One of the biggest advantages of HDRs is their editing capability, which is not available on tape decks for the most part (unless you like editing with a razor blade). Typical editing functions let you cut, copy, and paste sections of digital audio. When you copy and paste a section of digital audio in a nondestructive system, the data is not actually copied and pasted. Instead, pointers are used to play the data at any moment you want during the song. This lets you record a short riff and repeat it as many times as you want without using up valuable storage space. Similarly, when you cut a piece of data, the data is not actually erased from the disk, only the pointer to that data. You can also merge the data in several tracks to one track so they all play back together.

Other common editing functions include fade ins, fade outs, and crossfades between different sections of data. Normalization adjusts the amplitude of the material so the highest peaks correspond to the system’s highest allowable level to maximize the signal-to-noise ratio. You can also reverse a section so it plays from back to front.

In most cases, these operations are nondestructive. If you edit a piece of data and you don’t like what you did, you can undo it, and the original material returns unchanged. A few operations might be destructive, but the HDR will typically warn you of this before it proceeds with the operation.

Most HDRs include various effects-processing operations that can be applied to any section of the data. These include reverb, delay, chorusing, flanging, compression/limiting, and EQ. In many cases, the effects can be applied in real time as the data is playing back. This is much like sending the audio through an outboard effects processor.

In other cases, the computer must take some time to process the data with the desired effect. In this case, you must wait for the computer to finish its processing before you can play the material. This is sometimes called offline processing, which is often destructive, but the computer typically warns you before it proceeds.

Computer-based HDR software often accepts ancillary programs called plug-ins, which let you add various forms of signal processing. For a complete rundown on plug-ins, see "The Budget Desktop Studio" in the September 1996 EM.

In the end, you will probably want to mix your tracks and record them onto a stereo master tape. Most HDRs include their own internal mixer. In computer-based HDRs, the mixer appears on the screen. The faders and other controls can be manipulated with the mouse, but this is inefficient and sometimes impractical. It’s much better to use a MIDI fader box or other dedicated mixing surface, such as JLCooper’s FaderMaster or CS-10 or Peavey’s PC 1600. Mixer manipulations can usually be stored and recalled during playback, which provides automated mixing.

Some M-HDRs, such as the Roland VS-880, include a physical mixing surface, which makes it easy to mix. Other M-HDRs, such as the E-mu Darwin, have an internal mixer with no physical controls. In this case, the mixer is controlled from a MIDI fader box or computer software. Because the internal mixer and effects are usually digital (i.e., the digital signals never leave the digital domain), there is none of the degradation of signal quality that so often accompanies conversions from analog to digital and back again.

CARE AND FEEDING

Despite their popularity, hard disks are finicky creatures; they crash and corrupt data. As a result, it’s critical to back up your data regularly (preferably after each and every session). Removable cartridges provide the easiest solution; if your primary storage crashes, the cartridge can be used immediately. You can also use a data DAT deck, but in that case you have to restore the data to a hard disk before you can use it. Many modern computers and some M-HDRs include a SCSI port, which lets you connect an external device, such as a removable-media drive or data DAT deck. (Some PCs require an add-on SCSI card.)

A few systems let you back up to an audio DAT deck or MDM, such as an Alesis ADAT or TASCAM DA-88, but this also requires that you restore the data, and it’s a bit of a kludge. For example, the Fostex DMT-8 has no SCSI port, but it backs up two tracks at a time to audio DAT via the S/PDIF digital audio outputs. The Digidesign HDR systems can also back up to audio DAT using a program called DATa. This program backs up the playlist information followed by the actual audio data, all of which is sent to the DAT deck from the digital audio outputs on the interface hardware.

As you record and edit material, it is stored in different places on the disk. If data already exists on the disk and the system is unable to write an entire file in one contiguous area, the data must be stored in bits and pieces that are reassembled by the computer upon demand. Eventually, the data is so fragmented–spread out–that the computer can no longer find it efficiently. This also occurs when you do a lot of destructive edits, resulting in data being added and deleted. If the data becomes fragmented enough–and this can happen surprisingly quickly–disk access is slowed, and eventually crashes can occur.

As a result, the disk should be defragmented or optimized every so often, depending on how much you use the system. (Defragmenting puts each file in a contiguous space; optimizing not only defragments each file but reorganizes the entire disk so that data files are stored contiguously, applications are stored contiguously, and so on.) This is easy on a computer-based system; simply run a disk-maintenance program and defragment the disk. (Of course, make sure to back up the disk before performing the defragmentation; see "Desktop Musician: Don’t be a Crash Dummy" in the September 1996 EM.) Most M-HDRs defragment automatically or provide a method to initiate the process manually.

If you opt for a computer-based HDR, I recommend that you dedicate a separate hard disk to your digital audio data. Of course, you can record onto your primary hard disk, which also holds your operating system, applications, and other data files. But dedicating a hard disk to digital audio makes it easier and safer to defragment and back up the disk on a regular basis.

Affordable hard-disk recording is a great boon for musicians everywhere. This technology lets you record and edit audio with unprecedented ease and flexibility. All that remains is to try it out in your system.

Scott Wilkinson backs up his hard disk after every session to keep the crash gremlins away.