Digital Recording Devices

What are they?  How do they work? Which ones should I use?

Trevor Allan, Manager, Disability Services Unit, Australian National University &
Carl Runeson, Assistive Technology Officer, University of Wollongong

Contents

Background

In the good old days, audio recording was very simple.  The ubiquitous cassette player was the simple answer to most portable recording situations. The only major concerns were the type of recorder and whether you needed an external microphone. Controls were simple and intuitive, and everybody and his dog could learn to use one quite quickly. If you needed to record a lot of material, you simply needed to make sure you had enough cassettes to record on.

However, for all its simplicity and ease of use, the humble cassette had its limitations. The most obvious is that associated with any analogue device – linear recording. The material is recorded in a continuous line, and to find any particular part of that line, the tape has to be physically moved forward or backwards to find the relevant section. This means that finding material is time-consuming, imprecise and cumbersome. Linear recording is fine if you simply want to start listening and then listen all the way through until the end. Anything else is problematic.

Another problem with cassettes is that they are difficult to transfer to a computer or other device. The recording has to be played back in real time and a means of transferring it to the computer needs to be established. Copying tapes is time-consuming (even with high speed copiers), tapes get tangled and twisted in the machines, heads get dirty, complicated mechanical tape transport mechanisms break down and so on. It is not possible to use Voice Recognition to transcribe cassette tapes directly. Also, if a copy is needed, tape to tape copying degrades the quality of the signal.

Enter the Digital Recorder! No tapes to tangle, degrade or break. Files can be easily transferred to computers and other devices such as MP3 players. Copying recordings is fast, easy and simple. Recordings can be located on the web, they can be bookmarked, edited and divided simply and quickly and so on. Digital Files can be named and filed in a manner that doesn't take as much physical space as tape. In most instances, it doesn't take any more physical space at all - just memory space on a computer drive.

These, and many other advantages of digital audio recordings have seen the explosion of digital devices recently, with an associated explosion in the range, types, functions and quality of devices. To try to clear up some of the confusion around digital recording devices, The Australian National University and the University of Wollongong agreed to a joint research project to investigate the range, effectiveness, functions and applicability of different digital audio recording devices.

 

 

Types of Digital Audio Recorders

The types of Digital Audio recorders tested fall into the following categories:

• Digital Voice Recorders (DVRs) – these are the close cousins of the old cassette recorders. They are dedicated to the sole purpose of recording audio. They are quite compact, simple and effective in their sole function. They have:
• an inbuilt microphone (usually switchable in range and quality),
• separate input for an external microphone
• the capacity to switch between different recording qualities and recording capacity (The higher the quality, the shorter the recording capacity)
• the ability to organise  recordings into folders and files,
• the capacity to transfer files to computers like any other files,
• are compatible with Voice Recognition transcription requirements (particularly format)
•  usually record in the higher quality .wav format
• are simple and straightforward to use,
• usually have inbuilt speakers and headphone sockets
• Storage capacity is much higher than tape machines and are smaller in size (as are most MP3 recorders).

 

Flash MP3 Recorders – these are compact, relatively small capacity recorders that use an inbuilt Flash disk to store recordings. They are cheap, readily available and popular for storing music in MP3 format, with audio recording a secondary function. They usually have:

• No speakers (headphone only listening)
• Usually small controls and screens
• Disk capacity varying from 64 MB to 2 GB
• Inbuilt microphone
• Usually no external mic or Line input
• No moving parts

Figure 2: Techworks 256 MB Flash Disk MP3

 

• no speakers or small speakers
• large storage capacity
• external mic or line input
• larger controls
• larger, colour screens
• longer recording times
• some have variable recording quality
• multifunctional capacity (e.g. portable hard drive)
• Can often store and view video and text files

Figure 3: iRiver H10 20GB Hard Disk MP3

Devices Tested

Device	Manufacturer	Model	Type	Capacity	Price (A$)
T30 MP3 Player	iRiver	T30	Flash	512Mb	189
H10 MP3 Player	iRiver	H10	Hard Drive	20Gb	369
GigaBeat MP3 Player	Toshiba	GigaBeat	Flash	512Mb	200
Muvo MP3 Player	Creative	N200	Flash	512Mb	200
H340 MP3 Player	iRiver	H340	Hard Drive	40Gb	480
Camera	Ricoh	R4	Flash	1Gb Flash card	600
Mobile phone	Sony Ericsson	K750i	Flash	2Gb Flash card	700
Palm PDA	Palm	LifeDrive	Hard drive	4Gb	700
Techworks	from OfficeWorks	256Mb	Flash	256Mb	40
US395 DVR	Panasonic	US395	Flash	128Mb	185
SanDisk	SanDisk	SDMX1-512	Flash	512	190

 

Outcomes

The old adage, "you get what you pay for" is only partially true digital recording devices.  Sometimes you can pay for things that you don't need, sometimes you can need things that you haven't paid for and sometimes the cheaper device may actually be a better option for a particular purpose than a much more expensive device.

For straightforward voice recording, the relatively inexpensive Digital Voice Recorder from Panasonic outperformed many more expensive items.  The quality of the recording could be set at the highest level, varied according to need and produced one of the best results across a range of tests.  If other functionality is not needed, the quality, ease of use and value for money makes this, and other similar recorders, a very desirable device for voice recording.  The switchable microphone, the variable quality, compact size and simple controls all add up to a very usable device in a variety of recording circumstances. 

The recording in the .wav format means that recordings from this type of recorder can be used for direct transcription into voice recognition programs such as Dragon NaturallySpeaking. However, it should be noted that Transcription from recordings will produce lower accuracy rates than direct dictation using a headset microphone (see below) and it is very important to have the best quality signal to transcribe. Tests also indicate the benefits of using Auto Punctuation when transcribing from audio recordings.

The capacity to use external microphones for different situations is an additional benefit that allows for good quality recording in a variety of situations.

The Flash Disk MP3 recorders are very compact, light and simple to use.  While they do not have the flexibility of other devices and controls and screens tend to be quite small, they have their uses and in some cases they are the best and most appropriate choice.  They are small enough and light enough to hang around the neck of a speaker, providing a very usable recording.  The relatively low quality of recordings to enable much longer recording times on smaller capacity devices, poorer quality microphones (matched with the inability to provide better quality input through external microphones). Generally, the quality of recording is such that it is not suitable for Voice Recognition transcription.

The small size does have some major disadvantages, however, with tiny controls and screens making it very difficult for some people to operate, either through manual dexterity issues, or difficulties seeing the detail on the generally miniscule screen.

Hard Disk MP3 Recorders

Hard disk MP3 recorders generally have longer recording times, and often better audio quality than Flash disk recorders. The larger size, larger colour screens and versatility create a very tempting package.  Along with the audio recording capability, they can also operate as a very portable hard drive, transferring files between computers, downloading music files etc.  One downside of this versatility and functionality is that they tend to be a little bit more complicated to operate than the relatively more straightforward Digital Voice Recorders.  To access the voice recording, you need to scroll through various menu items, and know how to navigate through the various functions.  Another is the cost -- these devices cost 2, 3 and 4 times as much as a DVR or Flash disk MP3.

However, for some people, hard disk MP3 recorder is an ideal device, since it is able to meet many needs in a single package.  For example, a vision impaired user may store document files on the hard disk, download converted audio files for later playback, record live audio and store their music library on the same device.  Users would also have to work out how to navigate their way through the files and menus. Until version 9 of Dragon NaturallySpeaking, MP3 files were not suitable for transcription purposes.  We did experiment with converting MP3 files to wave files and then performing a transcription, but the results were not particularly satisfactory.  We have not yet tested MP3 transcription with version 9, but will do so in the near future.

Multifunction Devices

The Palm Lifedrive has quite a useful audio recording capability along with its usual PDA functions.  It has a built-in microphone, but no capacity to add an external microphone or line in input.  The quality of recording from a reasonably loud close-up signal is quite usable, but the capacity to record in difficult environments is limited.  A weak original signal, noisy environments and distance from the microphone all reduce the quality of the recording quite dramatically. The built-in speaker is quite tinny and distorts quite readily.  It is useful mostly for checking the existence of recording rather than listening to lengthy passages.  The quality of signal through ear buds or headphones is significantly better.

Like hard disk MP3 recorders, the Palm LifeDrive can function as a portable hard drive with its 4 GB storage being able to store files, documents and photos.  The organisational benefits of having calendars and schedules may benefit some people with organisational difficulties such as Asperger’s or ADHD.  Reminders and deadlines can be scheduled with an automatic notification prior to the deadline.  It also allows synchronisation of schedules and documents between computer and PDA.

As can be seen from the table below, the bit rate of the LifeDrive is similar to that of Flash disk MP3's, which poses some issues with recording quality.  However, a high compression rate and large storage capacity means that it has very long recording time capability. Not suitable for Voice recognition transcription.

The Ricoh Camera is able to record live audio, but again the quality and limited storage space restricts its usefulness as an effective audio recording device. However, with a 1 GB Flash card, the recording time expands dramatically to 2115hours. Not suitable for Voice recognition transcription.

The Sony Ericsson Mobile Phone again has limited usefulness and mostly curiosity value.  High compression rates equal longer recording time on limited storage capacity, but at the price of reduced quality.  It is designed for mostly close-up use, with no capacity to use an external microphones or line inputs.  With the right software and connections, it is possible to transfer these files to and from a computer, but the usability is limited by complexity and quality issues and if you are looking for an effective audio recording device, there are much better options available at much more reasonable cost. Not suitable for Voice recognition transcription. A Nokia mobile phone was also tested, but there was no means of connecting to a computer, and there was also a 1minute recording limit, so was deemed unsuitable.

Conclusion

For simple, straightforward and effective audio recording, flexibility, ease of use and value for money it is hard to go past Digital Voice Recorders such as the Panasonic we tested.  Most people could learn how to operate the devices very quickly and effectively and quality of recording is better than most alternatives.  The connectivity to computer via USB cable and bundled software is effective and simple and most DVRs offer a capacity to transcribe speech to text through voice recognition software such as Dragon NaturallySpeaking. It is possible to organise recordings into folders for structural and filing purposes quite readily and simply.

As an all-round digital recording device for someone who only wants to record audio, they are probably the best value/performance/functionality choice. Even when the money is taken out of the equation, they are still a better choice for recording audio only.

• For general recording purposes, where recording environment may be variable or less than optimal.
• Where external microphone is needed
• For Voice Recognition transcription
• No need for other functionality (e.g. portable data storage)

Hard Disk MP3 Recorders are the next choice in terms of quality. With Bit rates of up to 320 kbps, compared to 32 to 64 kbps for most Flash Disk recorders and Multifunction devices. This compares to 352 kbps for the US395 at HQ and 256 kbps at the lower quality. They can go as low as 40kbps, similar to Flash Recorders. There is a much greater variation in quality with these recorders, depending on the settings chosen. Lower rates will give longer recording times, but at the expense of quality .These devices have the added advantage of greater flexibility & functionality than a DVR. They are able to function as a portable Hard Drive, store and display photos and video, MP3 music, etc. This could be of benefit to some users, such as a person with a Vision Impairment, who could use such a device to store text material, electronic texts, audio recordings and text to audio transcriptions. This could be a distinct advantage, being able to use one device instead of several different devices performing different functions, such as USB Drive, Audio Recorder, CDs etc.

Most Hard Disk MP3 recorders are also able to store and view video and text files.

They usually have colour screens that are much larger than the Flash MP3 recorders, but also have larger overall dimensions, controls and screens. This can be a problem if small size is desired, but are easier to manipulate, and the larger, colour screen is easier to distinguish. These devices also cost more - usually in the range of $450 to $600.

Where good recording quality and flexibility is needed, the Hard Disk MP3 recorders can be a viable alternative to DVRs and other devices.

INDICATED USE:

Flash Disk MP3 Recorders have their place, even though the quality of recordings are usually much lower than DVRs or Hard Disk MP3 recorders. For straight audio recording in a relatively quiet environment, with a strong signal, they can produce quite listenable recordings. For dictating directly into the recorder, or hanging around the neck of a speaker, these recorders would work quite well. However, for more noisy or challenging environments (e.g. a person speaking some distance from the recorder, or a large meeting) the results (see below) may be less than is needed for clear recording. because the initial quality is so low, any detrimental aspects of signal or environment will significantly affect the usefulness of the recordings.

They are cheap, readily available and highly portable. If the user is able to see the screen, use the small controls and appreciates the compact, unobtrusive nature of the devices in good recording environments, they could be a very effective audio recording device.

• For general recording purposes, in good recording environments (strong signal close to device, etc.)
• Not suitable for external microphones
• Where compact, portable recording needed
• Where cost is a major factor
• Where major use is listening to recordings
• Need to be able to regularly transfer recordings to computer due to more limited storage space
• Not suitable for Voice Recognition transcription
• For students who need basic recording functions only.

PALM LifeDrive is an excellent PDA, with many features, functions and excellent (4GB) storage. The audio recording function is useful in good recording situations and can be very beneficial in situations where having a single device for a range of functions is important. Like the Hard Drive MP3 Recorders, it can function as a portable Hard Disk, PDA, photo storage and display unit and digital audio recorder. Comments for the LifeDrive in audio recording situations are similar to those for the Flash MP3s - it is a similar recording quality, and, although the price is significantly more, the range of functions and usability is also much wider. While it is not a device I would purchase for its audio recording capability alone, it is a valuable and quite useable extra function that increases its appeal as a PDA. It has a large colour screen, with touch controls, on screen keyboard and manual controls. It also has the capacity to connect to an external Infra Red Keyboard.

INDICATED USE:

Note on Convergent Technology.

The days of separate devices for different purposes such as audio recording, data storage, camera, mobile phone, etc is starting to disappear. The emergence of Convergent Technology, where devices perform a multiplicity of functions, is increasing. When these devices first started appearing, they tended to perform their main function reasonably well, and a number of other functions quite poorly. However, the developments have been very rapid, with quality improving, significant increases in capacity, usability and effectiveness coming thick and fast. Devices like the Palm LifeDrive, Hard Disk MP3s and a number of mobile phones, are blurring the boundaries. There are still gaps, like the lack of external microphone or line inputs, but these devices are getting better with each incarnation.

Hopefully the day will soon come when a device will appear that can do all functions with equal quality and accessibility, with all the desirable features of the earlier technologies included. For example, the effectiveness of my LifeDrive would be substantially increased if the manufacturers included a very simple, low cost "Microphone In" socket, so that a user would have the option of specialist microphones for more challenging recording situations. It is very frustrating to be very impressed with a particular device, only to find it lacks a particular feature that restricts its universality.

TEST DATA

Panasonic US3595 Digital Vice Recorder

Internal Mic	External Mic	FM Radio	Batteries	Recording Format	Min Rec Rate
yes	yes - 3.5 plug	no	Yes 2 AAA	Wav	128Kbps

Max Rec Rate	USB Interface	Min Rec Time	Max Rec Time	Battery Life
352Kbps	Standard	19 Hours 30	66 Hours 50	11.5 H recording 19.5 H

Test results:

Default Sampling Rate - No Mic

These files were transferred over from the Panasonic with the default sampling rate

HQ-16             FQ-16             SP-8

SP Meeting	quite distorted, compression artifacts very obvious, can hear what is said (just)
HQ Meeting	good recording, quite a bit of background noise
HQ Dictation	good recording, little background noise
FQ Meeting	quite distorted (less than SP meeting) can hear what is said, compression not so obvious

Highest Sampling Rate - No Mic

These files were transferred over from the Panasonic with the highest sampling rate

HQ-22             FQ-11              SP-11

These files were marginally better than those transferred over at the lower sampling rate. The lower resolution recordings suffered the most from the difference in transfer resolution but the difference is hardly discernable when comparing the higher resolution transfers.

Meeting

Meeting Internal mic	background noise, difficult to hear
Meeting Cheaper Sony mic	higher tone than above but more distorted, background noise
Meeting Expensive Sony mic	a bit clearer than above but still difficult to hear

Dictation - Default transfer resolution

Dictation Internal mic	less noise than meeting setting but a bit difficult to hear
Dictation Cheaper Sony mic	some noise but soft recording, difficult to hear
Dictation Expensive Sony mic	a bit clear than above, can discern better

 

Dictation - Highest transfer resolution

Dictation Internal mic	clearer than that transferred at default resolution
Dictation Cheaper Sony mic	higher tone recording a bit more listenable than above, slightly quieter recording
Dictation Expensive Sony mic	soft recording but easier to listen to, some distortion noise but less than others

Voice Recognition Transcription Panasonic US395 (Carl Runeson)

Using the poem The Puddin' Thief (Norman Lindsey) as a reference I created a user file with the Panasonic. Below are the results from using Dragon naturallySpeaking Professional Version 8 to transcribe from these recordings.

A dictation test with the internal microphone gave an accuracy of about 15%

A dictation test with a cheap microphone gave an accuracy of about 25%

A dictation test with the expensive Sony microphone gave an accuracy of about 35%

Using the poem The Raven by Edgar Allen Poe

A dictation test with the expensive Sony microphone gave an accuracy a little over 80%.

Summary.

The upshot of testing the Panasonic RR-US395 is that you really need to speak clearly and loudly and very close to the microphone to be able to use the voice recognition software with it at all. This finding seems to be supported by the literature on the internet. The best response was with using an external (Sony) microphone.
It may be that in the future with higher capacity devices the bit rate quality may be able to be increased leading to better voice recognition. As it stands I would personally not use a digital recorder with Dragon - I would use a USB microphone plugged into the PC running the software in preference.

Other MP3 Players

The recordings were performed in Room 203. Room 203 is a medium sized room suitable to seat about 20 to 30 people in a small lecture/tutorial type setting.

The recorders were all placed on a table and then turned on and set to start recording. The recordings consisted of me reading out "The Raven" by Edgar Allen Poe while walking from the recorders around the room and behind the recorders for the length of the recital of the some of the poem. An exception to this was the Toshiba GigaBeat which had lost its battery power over the three days since it was fully charged and was done at a later stage with condition similar to the other tests.

DEVICE	RESULTS
Creative N200 Internal mic	very soft recording, not really discernable, not a lot of background noise though
iRiver H10 Internal mic	good recording (bit soft) but a high pitched background noise
iRiver T30 Internal mic	softer recording (than above) a little background noise (not a problem though)
Toshiba GigaBeat Internal mic	OK recording but an annoying buzzing noise
iRiver H340 Internal mic	good recording (stereo), some background noise
iRiver H340 Cheaper Sony mic	good recording, less noise than above
iRiver H340 Expensive Sony mic	very good recording, crisper than above, a little noise (not annoying)
SanDisk internal mic	dull record, indiscernible at a distance of more than 1m
TechWorks 256 MP3 Player	reasonable good recording for the resolution
Ricoh Caplio R4 Internal mic	a lot of noise, dull recording but listenable
Sony Ericsson k750i internal mic	soft recording, no good at a distance of more than 1m
Palm LifeDrive	noisy recording, voice barley discernable

Note: Sony Ericsson recordings converted using Sony Ericsson conversion software which converts (up) to 128kbps.

Bit Rates of recordings at highest settings

DEVICE	BIT RATES
Creative N200	32kbps (there doesn't seem to be any way of changing this setting)
iRiver H10 Internal	128kbps
iRiver H340 Internal	128kbps (lowest setting for H340 is 40kbps)
iRiver H340 External	320kbps
iRiver T30 Internal	128kbps
Toshiba GigaBeat Internal	192kbps
SanDisk internal mic	32kbps (can’t seem to change this either)
T echWorks MP3 256 Player	32Kbps
Ricoh Caplio Internal	l 64kbps
Palm LifeDrive	33Kbps
Panasonic Digital Recorder	Highest possible transferred recording is 352kbps HQ setting (transferred at 22Khz with packaged voice editing software) Conversion with a 16Khz settings gives a 256Kbps recording.

 

A test was conducted using a H340 as the digital recorder using its internal microphone recording at 128Kbps (44Khz, 16 bit). The H340 records in MP3 format so the files had to be converted to a mono wav file. The Creative Audio Converter (that comes free with the purchase of a Audigy USB sound “card”) was used for conversion. Several attempts were made at creating a voice file for setting up Dragon but all attempts created files with an inappropriate signal to noise ratio usually between 12 and 14. bearing in mind that the H340 is not designed for this kind of work. The accuracy was about 65%. The setup voice files were recorded in environments with some background noise in one case a noisy air conditioner and in the another case a very noisy laptop. This could have contributed to the unsatisfactory signal to noise ratios.

Note: The different devices record at different bitrates.

Phone quality is considered about 64kbps at 8Khz sampling, a cell phone is 13kbps at same sampling rate

The more expensive Sony microphone is definitely better than the cheaper model.

The line-in on the GigaBeat and iRiver could not be used with an external microphone as one can on the H340. A powered microphone is needed. Using one negates the advantages of portability the MP3 player affords.

Microphone recording wasn't even tried on the Creative n200 as the connector is the smaller 2.5mm which I have no connections for.

General Notes:

The Technician speaks:

"I thought I would just explain the possibly obscure choice of reading material. As I was going to be reading this stuff out over and over again I thought I would choose something that would present a bit of a challenge to the voice recognition software but was also going to be something I would enjoy reading, hence the choices. It really makes little difference apart from highlighting that some dated language will be a challenge to voice recognition as the accuracy was measured against the same texts.

A group of programmers have hacked some of the iRiver, Archos and iPod devices to come up with an alternative User Interface (UI) which may be of use to people unable to use the physical controls, such as a voice user interface (I haven’t tried this yet but may do it soon with my iRiver H340)

More information at: http://www.rockbox.org/twiki/bin/view/Main/FeatureComparison

iPods were not considered in this review as voice recording is not standard on these devices. Voice recording can be facilitated on these devices with the help of external hardware. Adding external hardware does wander away from the benefits of ease of use and portability and using the one integrated unit."

Features:

iRiver T30 Flash MP3 Recorder 512 MB

Internal Mic	External Mic	FM Radio	Batteries	Recording Format	Min Rec Rate
yes	no Line In	Yes	Yes 1AAA	MP3	40Kbps

Max Rec Rate	USB Interface	Min Rec Time	Max Rec Time	Battery Life
128Kbps	Standard		6 Hours 20	Up to 20h

Toshiba GigaBeat Flash MP3 Recorder 512 MB

Internal Mic	External Mic	FM Radio	Batteries	Recording Format	Min Rec Rate
yes	no Line In	Yes	Rechargeable	MP3	32Kbps

Max Rec Rate	USB Interface	Min Rec Time	Max Rec Time	Battery Life
192Kbps	Standard			Up to 14h

Techworks MP3 Recorder 256 MB

Internal Mic	External Mic	FM Radio	Batteries	Recording Format	Min Rec Rate
yes	no	Yes	Yes 1 AAA	MP3	32Kbps

Max Rec Rate	USB Interface	Min Rec Time	Max Rec Time	Battery Life
32Kbps	Standard	17 Hrs 30	17 Hours 30	Up to 10h

SanDisk Flash SDMX1 -512 Disk MP3 Recorder 512 MB

Internal Mic	External Mic	FM Radio	Batteries	Recording Format	Min Rec Rate
yes	no Line In	Yes	yes 1 AAA	MP3	32Kbps

Max Rec Rate	USB Interface	Min Rec Time	Max Rec Time	Battery Life
32Kbps	Standard	25Hrs 35	35 Hours 35	Up to 15h

Creative Muvo N200 Flash Disk MP3 Recorder 512 MB

Internal Mic	External Mic	FM Radio	Batteries	Recording Format	Min Rec Rate
yes	no Line In	Yes	yes 1 AAA	MP3	32Kbps

Max Rec Rate	USB Interface	Min Rec Time	Max Rec Time	Battery Life
32Kbps 192(LI)	Standard			Up to 15h

River H10 hard Disk MP3 Recorder 20 GB

Internal Mic	External Mic	FM Radio	Batteries	Recording Format	Min Rec Rate
yes	no Line In	Yes	Rechargeable	MP3	32Kbps

Max Rec Rate	USB Interface	Min Rec Time	Max Rec Time	Battery Life
128Kbps	Standard	337 Hrs 12	1348 Hours 50	Up to 16h

iRiver H340 hard Disk MP3 Recorder 40 GB

Internal Mic	External Mic	FM Radio	Batteries	Recording Format	Min Rec Rate
yes	yes - Line In	Yes	Rechargeable	MP3	40Kbps

Max Rec Rate	USB Interface	Min Rec Time	Max Rec Time	Battery Life
128Kbps 320 (Line In)	Standard			Up to 16h