Audio Hard Drives - How To Choose

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It may not be immediately apparent, but audio hard drives are possibly the most important part of any DAW other than the soundcard. Read on for the audio hard drive tutorial.

Obviously hard drive size is important so you can keep as much digital audio as possible on the drive, but what about other factors such as speed, noise and reliability?

In this article we’ll examine the importance of hard discs to the audio engineer, and how you can go about choosing a new drive or optimising the one you already have.

Due to the advances in IDE technology and the new SATA interface, we will not consider SCSI devices due to their cost, need for dedicated controller and limited benefits over the newer ATA and SATA drives.

Digital Audio Data Rates – The Basics

Firstly, let’s look at digital audio. Most of you will be recording at a sample rate and resolution of at least 16 bit/44.1kHz. How does this translate into MBs? Well, let’s look at the maths:

Bit Depth x Sampling Freq.

16 x 44100

This gives us;

705600 bits

We’ll want to convert bits into kilobits so we need to divide by 1024;

705600

1024

This results in 689 Kbits.

Now, let’s converts kilobits into kilobytes by dividing by 8;

689

8

This gives us a figure of 86 KB/s

86 KB/s doesn’t sound too much does it? Well, no, but let’s see how it translates into 3 minutes of recording;

86 x 180 (secs) = 15480 KB/s

Let’s convert that into MBs

15480

1024

So we have a figure of

15 MB

Ok, that’s a larger figure but still nothing to lose sleep over I hear you cry.

Well let’s now say that we’ve recorded a 3 minute song with 16 mono tracks.

15x16=240MB

So that’s roughly quarter of a GB, and that’s presuming that we delete all takes not used and all files are mono (stereo tracks are, logically enough, twice the size)

You can see here the size starting to increase, and this is presuming you’re writing nice 3 minute pop ditties – if your compositions are 10 minute prog rock epics then you can see this figure growing much larger!

Digital Audio can rapidly eat into your Hard Drive space

On top of this we’re presuming that we’re working at 44.1/16 here. If you’re working with higher bit depths or sampling frequencies then the figures are larger;

* - the 16bit/48k format has been included as this is the rate most Creative Labs cards function at by default

What’s clear from our findings above is that digital audio is quite greedy in comparison to other file types, and if you record frequently then you could soon see your free space dwindling quicker than Leeds Uniteds finances.

However, as well as the size of these audio files we have to consider another factor…

The need for Speed

If size was the only consideration we could all just buy big hard drives and get on with recording, but we also need to bear in mind how quickly our drives can read and write the information.

 A 300GB drive would be of little use if it could only supply data at 1MB/s – that would only allow us to run about 12 simultaneous tracks of mono 44.1k/16-bit audio before the audio starts to falter. (1024/86 = 11.9)

Therefore, when considering a hard drive it is important to give equal, if not precedence, to the speed of the drive.

If you want to test the speed of your current drive there are many different applications available which can benchmark your drives. One of the most popular is the SiSoftware Sandra benchmark suite which allows you to benchmark most elements of your PC. However, for the home musician the most useful is probably Dskbench which translates the results into the number of tracks you can run on your system.

With hard discs so cheap now, it’s not out of the question to install an audio only hard drive in your PC to take the strain off your main drive, and reduce the likelihood of any interference from Windows whilst you’re recording the perfect take!

Audio Hard Drive Basics

When looking for an audio hard drive for your DAW, there are several factors that are important;

Size – This is expressed in Gigabytes, and drives of up to 250Gb are on the market as of the time of writing.

RPM – this is the speed of the drive in terms of how quick it spins. The most common speeds are 5,400rpm & 7,200rpm, although the new SATA format is producing drives with speeds of 10,000rpm. The quicker the drive spins the quicker information can be read from the drive, although higher rpms may also result in higher noise levels (see below)

Transfer Rate – This is the really important figure. Many manufacturers will include information such as ATA100 in the product description. The numbers in these descriptions represent the (theoretical) maximum speed of the drive in MB/s. So an ATA133 drive can theoretically shift data at 133MB/s. However, there are 2 limiting factors here. Firstly, your motherboard has to support the relevant ATA ‘speed’. If your motherboard only supports ATA66 for instance, any ATA100 or 133 drives will not exceed a speed of 66MB/s.

Secondly, these figures only really represent the ‘burst rate’ which is the maximum data transfer rate, not the sustained rate. Most of the time the sustained rate will be around 75%-80% of the maximum speed, but it can be even lower depending upon the setup of your PC.

Seek Time – This is the amount of time, in ms, that it takes the drive to find the required data. Shorter values are preferable.

Cache – The cache, sometimes called a buffer, is a ‘storage area’ whereby data is held until it is needed by the PC. Data can be read very quickly from the buffer. A drive with a large cache will ensure that any short-term slowdown in data transfer does not result in a loss of audio as there will already be data stored in the buffer.

Interface – By far the most common (at least at the time of writing) is the IDE interface. This is supported on all but the oldest motherboards and is a mature protocol. It comes in a few flavours, ATA66/ATA100/ATA133. As explained above, these refer to the maximum possible speed of the drive in MB/s. However, your motherboard also needs to support the same ATA value to get the best performance. The second interface available at present is SATA. This is a serial rather than parallel interface and can offer speeds (theoretically) much higher than standard ATA/IDE. It also uses much smaller, and easier to handle, cables. Only newer motherboards (those made in the last 6-8 months) offer this interface, although this will probably replace IDE completely in the near future.

Noise – If your PC is in the same room that you record in, then you’ll obviously want to keep the noise down to a minimum. Not all manufacturers reveal the noise of their drives, but those who do will probably express the noise of the drive in dBA.  Usually faster drives (in terms of RPM) will be louder but some manufacturers produce quiet drives using specialised components to reduce ambient noise levels. Obviously the lower the figure in dBA the better.

Installing your Audio Hard Drive

The physical act of installing an audio hard disc is not challenging at all, especially with the new SATA format, and it can be performed by someone with little or no PC knowledge.

Before you get your hands dirty, you’ll want to consider how the drive is going to fit into the PC in terms of IDE channels.

Most motherboards will offer 2 IDE channels, each allowing 2 devices to be connected to each channel, one as a ‘master’ and one as a ‘slave’. There are a few considerations to make when deciding where to put your audio drive.

Although most motherboards are intelligent enough to handle the IDE bus without causing problems, it’s best to err on the side of caution in my personal opinion.

I would recommend setting up the audio drive as the master on the secondary IDE channel with the system drive the master on the primary IDE channel. Presuming you have two CD/CDR drives in your system, then put the drive that is least likely to be used at the same time as you are recording on the secondary slave, and the remaining drive on the primary slave. A common configuration is;

It’s also worth noting that if you have a CD/CD-R drive on the same channel as your audio drive, it’s a good idea to disable ‘autorun’ on your system (although this is less of a factor in Windows XP than previous versions of Windows)

With SATA, hard drives won’t be sharing channels with CD devices so you have a bit more freedom.

You will also need to format your hard drive, to make it accessible from Windows. If you’re running Windows XP/2000 then NTFS is the obvious choice. For older versions FAT32 is the best option.

RAID – Is it worth it?

Some motherboards, especially the newer SATA ones offer RAID functionality. RAID is a method of using more than one drive to store data in a number of different ways. Ideally in RAID arrays, you should use identical drives in terms of manufacturer, size and speed.

Although there are several RAID configurations, we’ll make things simple and look at the 2 main options - ‘striping’ and ‘mirroring’.

Mirroring – This RAID type basically mirrors all the data being written to another drive, so if you have a hard drive failure you will have perfect backup on the other drive.

Striping – This enables Windows to see your 2 (or more) drives as one large drive. Not only does this offer a large ‘virtual’ disc, it also offers a very quick transfer rate (as the 2 drives are writing independently). This can effectively double your simultaneous track count which is especially useful if recording at 24-bit/96kHz.

Most people won’t need the Mirroring capabilities unless (a) the material is very critical (i.e. commercial projects) and/or (b) they can afford 2 drives but only effectively use one.

Striping on the other hand is very popular in specialist audio computers as it increases both the amount of data that can be stored and the number of tracks that can be recorded/played back.

If you like to use higher sampling rates and/or you need hundreds of audio tracks simultaneously then Striping is a good option, especially with SATA drives.

One word of warning though: some current motherboards operate with their RAID chip sharing the PCI bus. This means that the PCI bus can ‘max out’ under stress especially if your PCI soundcard is also transferring data at the same time.

If you wish to go down the RAID route, then look for a motherboard that does not share the PCI bus with the RAID array. This information is not always made readily available to the punter so if in doubt email the retailer or manufacturer to clarify the situation.

To Partition or not to Partition?

Another common ‘tweak’ is the use of partitions on the audio drive (we’re not talking about partitioning the system drive here for a multi-boot system – that will be covered at a later date)

The advantages of this may not be immediately obvious, but yet it is quite logical.

The fastest ‘part’ of a hard drive is the outer edge, so therefore it would make sense to force your computer to record onto the fastest part of the drive.

The solution to this is to create two partitions on your audio drive: one for ‘active’ projects and one for ‘finished’ projects. So with a 120GB drive for instance, you could create a 40GB partition to record onto and then an 80GB partition to move your projects over to when they’re finished.

This will ensure that your active projects will always be using the fastest part of the drive, and when you’ve finished recording and mixing down you can move the project over to the larger partition.

Partitioning your hard drive is a simple process and can be performed in Windows itself via Disk Management.

Start->Settings->Control Panel->Administrative Tools->Computer Management->Disk Management

A more common, albeit expensive, method is to use the popular software package Partition Magic by Powerquest.

Powerquests Partition Magic is a favourite amongst PC users.

Optimising Your Audio Hard Drive

Whether you’ve installed a new audio drive or you use your system drive for your recording, you can still optimise the performance of your DAW with some general housekeeping on your hard discs.

The first, and most important, ‘tweak’ is to regularly optimise your audio hard drive by de-fragmenting it. As your audio drive gets used over time, and files are constantly created and deleted, it’s not always possible for Windows to store files in a continuous manner. This means that files can be broken up and stored all over the disc which can slow down the reading of files as the system has to write for the drive to find the next part of the file.

A Fragmented drive can compromise the speed of your system

De-fragmenting ensures that your files are stored in a logical way which increases the efficiency of your DAW. Although the NTFS file system is less prone to fragmentation than FAT32, it’s still worth fragmenting your audio drive regularly (and your system drive if you don’t already) When running defrag applications, ensure there are no applications such as virus checkers running in the background as these can prevent the de-fragmentation from taking place.

In software such as Partition Magic, you can set a ‘cluster size’, in kbs, for your audio hard drive. Clusters are a set of number of kbs that hold data on your PC. The size of the clusters can have quite an impact on drive speed.

For instance, if you were to use a small cluster such as 2kb, then a large audio file would require many clusters which, unless the drive was continually optimised, could slow down the read speed of your drive.

However, if a larger cluster size, for instance 32kb, is used then not as many clusters would be required for a large audio file. It also prevents the drive from severe fragmentation. Of course, on a system drive a smaller cluster size would be preferable as there are smaller files present.

You will also want to ensure that Windows (or any of your applications for that matter) are not using your audio drive to store ‘temp’ files, swap files or hibernation states. Please refer to my Optimising XP for Audio article for more information.

Finally, when finishing projects, remember to delete any unwanted audio from the relevant folders. Sequencers such as Cubase have an audio pool which includes functions to remove unwanted files from the pool and therefore free up more disc space.

Author: Ben Morgan

XP AUDIO FORUM