AET 2050 - DAW Production

6. Data Storage Media - Interfaces

Objectives

1. Identify the different interface technologies used in DAWs
2. Give the basic specifications for these interfaces

Reading:

Chapter 5.2, Desktop Audio Technology - Rumsey

Interfaces - general

• All storage media is considered I/O to the computer.
• The media is accessed via an interface - a physical and logical specification for connecting the devices and moving data to/from the device.
• The interface speed will affect the overall throughput of a storage device.
• Interface speed defined as Mb/s or MB/s - know which is being defined!

Interface types

Serial ATA

The current standard for most new computers (Apple Mac Pro, for instance) using serial ATA (SATA).

• Pros of SATA
• Very fast - comparable to fastest SCSI interfaces
• Simpler interconnection due to serial design
• reduced cable-bulk and cost (reduced from eighty wires to seven), faster and more efficient data transfer, and hot swapping.

Serial ATA cable

Firewire (IEEE 1394) Interface

• Devised by Apple, the Firewire interface was created to provide a easy-to-use, extremely fast interface for computers and media devices.

Features:

• Serial transfer
• Capable of daisy-chaining up to 63 devices
• No ID's or termination is needed
• Hot swappable
• Power included - devices can be powered from the firewire cable
• Burst transfer rate is 400 Mbps (50 MB/sec) for original spec (1394a).
• 1394b spec increases the data rate to 800Mbps (100 MB/sec). Future rates will go to 1.6 Gbps.

Interfacing

• Firewire 400 utilizes two different connectors - a 6-pin which includes the power lines, and a 4-pin without power.

Firewire 400 connectors

• Firewire 800 uses a different 9-pin connector.

Firewire 800 connector

• The two versions can be mixed, with the use of proper adaptor cables.

Applications

• Firewire devices are generally high-capacity devices, such as drives or video cameras.
• Typical application, "Firewire drives" are boxes with firewire interfaces and ATA drives internally.
• Yamaha corporation developed the mLan spec to send multiple sample-accurate AS signals, raw audio, MIDI and other control information over an IEEE 1394 bus.
• By sending digital audio and MIDI information over a single cable, connecting will be simplified (YMMV).

USB (Universal Serial Bus) Interface

• USB is a serial interface designed to make peripheral connections to computers easier and more universal.
• Faster than older serial connections, and found on both Macs and PCs.
• Originally designed for peripherals such as keyboards, mice, printers.
• New 2.20 spec has faster data transfers (480 Mb/s), making it suitable for drives, cameras, and other high-speed or high-capacity devices.

Features:

• Serial transfer
• A USB connection scheme consists of one host and one or more USB devices. Configured in a "branch" topology.
• Up to 127 devices can connect to the host, either directly or by way of USB hubs.
• No ID's or termination is needed.
• Hot swappable
• Power included - devices can be powered from the USB cable
• Original spec (USB 1.1) defines data rates of 12 Mbps (1.5 MB/sec)
• The USB 2.0 spec ("hi-speed USB") increases this rate to 480 Mbps, and uses the same connectors and cables as USB 1.1

Interfacing

• USB cables have a different connector at each end, called type A and type B. The flat Type A connectors are used at the "upstream" (host/hub) end, and squarish Type B connectors are used at the "downstream" (device) end.

Type A connector     Type B connector

• Additional devices can be added by expanding the "branch" configuration with a hub.

from host      to devices

USB expansion hub

Applications

• USB was originally designed as an interface for lower-speed peripherals such as keyboards, mice, printers, etc.
• The hi-speed USB has expanded its use to hard drives and other high-capacity devices.
• USB has become commonplace for MIDI interfaces. The MIDI Timepiece is a USB MIDI interface that takes advantage of USB's asynchronous communication.
• USB is used for audio interfaces but is limited to six streams of 16-bit or four streams of 24-bit audio. (hi-speed USB allows expansion of this number).

 

ESATA

SATA meant for external connectivity. It has revised electrical requirements in addition to incompatible cables and connectors:

Few devices currently have Esata connectors natively (must be added through expansion cards to the computer)

Some single disks can transfer 131 MB/s during real use, more than twice the maximum transfer rate of USB 2.0 or FireWire 400 (IEEE 1394a) and well in excess of the maximum transfer rate of FireWire 800



The Future

USB 3.0's 5.0Gbit/S and Firewire's future 6.4Gbit/S will be faster than eSATA I, but the eSATA version of SATA III will operate at 6.0Gbit/S, thereby operating at negligible differences of each other.

OLDER TECH

ATA

• The ATA (Advanced Technology Attachment) bus interface was designed as the expansion bus interface for the PC.
• Originally also referred to as IDE (Integrated Drive Technologies).
• Most hard drives of just a few years ago (pre-2008) were interfaced with ATA/IDE.
• Parallel configuration.
• Designed for use "inside the box." i.e. internal

Configuration

• ATA is an internal-only system - no provision for external connections.
• Connection is made with a parallel cable between host and 1 or 2 devices. One device is configured as MASTER, one as SLAVE.

Pros of IDE/ATA:

• Inexpensive due to high volume of production.
• Increased speeds made it a viable choice for most computer systems.
• Fairly easy configuration.

Cons of IDE/ATA:

• Very limited device attachment (two drives (including CD-ROMs) per channel, and two channels per system max.)
• Wasn't designed for external attachment.  A drive couldn't be added without opening the box (tho this changed with External USB IDE interfaces ala
• 
• Single threaded (commands do not overlap even with a second drive)

Interface versions

• There are different versions of the interface, each with improvements over the others.
• One should be sure to note what interface is needed/used before adding devices!

SCSI (Small Computer Systems Interface)

• SCSI is a high-performance intelligent interface.
• For years, the highest performance - superior to ATA.
• It is a more complex system (internally) and is generally more expensive.
• Still gives highest performance for disk-intensive tasks such as servers or large digital audio projects.

Pros of SCSI:

• Flexible device attachment (up to 7 or 15 devices per SCSI bus) (inside or outside of case)
• Longer cable lengths allowed (up to 12 meters using LVD)
• Support for almost any peripheral type (disks, tape, CAROM, optical, scanner etc.)
• All commands can overlap with commands on other devices.
• Interface and protocol is carefully specified and regulated by ANSI.

Cons of SCSI:

• More expensive than IDE/ATA, due to more complex firmware and extra testing required. (Not to mention greater performance commanding a higher price).
• More complicated to install than IDE/ATA, due to addressing and termination requirements.
• Proliferation of improved formats can cause confusion related to "mixing and matching" of formats.

Important notes on SCSI:

• Numerous SCSI devices can be daisy-chained together: 8 for narrow and 16 for wide (the computer will take up one).
• Each device must be assigned a separate ID number.
• The last device must be terminated to prevent feedback.
• Mixing of types can be confusing and dangerous - care must be taken to ensure proper installation.
• For most applications, ATA or Firewire interfaces suffice, and are actually faster than the midrange SCSI interfaces. Serial ATA is now faster than all but the fastest SCSI interfaces, for example.
• Practically speaking, only the highest levels of SCSI (ultra-fast wide, for example) are used for the most demanding applications.
• While being surpassed today, SCSI is still used extensively in many studios where older technology is still present. Important to understand its use and application!

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