Recording Audio- Quality before convenience

-cap’n casper, founder

Attempting to capture electronic voice phenomena (EVP) remain one of the most popular activities for ‘ghost hunters’. While a laudable pursuit, when does having the newest gadget actually hinder one’s work? With the advent of small digital voice recorders, it seems that many investigators have sacrificed quality for convenience. These devices provide great flexibility, but many not provide the audio fidelity of other means of recording. So what should be used? Let’s take a look at some common devices and methods and see if we can come to some sort of conclusion.

For decades, magnetic tape was the predominant means of recording audio. Reel-to-reel recorders were used by the earliest pioneers of EVP, including Friedrich Jeurgenson, Konstantin Raudive, and others. At the time, these were the highest fidelity devices available and were capable of providing good results. Then came the development of self-contained magnetic tape cartridges. These cassettes made magnetic tape recording more accessible and easier to implement.  Low-end decks tended to be overly noisy, which led to the development of Dolby noise reduction. High-end tape decks are still readily available, and many can be purchased in a used condition for quite reasonable prices. DAT (digital audio tape) was one of the last iterations of magnetic media, utilizing a magnetic tape to store audio data much like the magnetic data backup media of the computer world. This description of the evolution of magnetic tape technology is of course, overly simplified and meant merely to provide a frame of reference for the comparisons to come.

Analog recordings using magnetic tape have the advantage of not altering the audio signal in any way (except in the case of DAT). The incoming signal is written directly to the magnetic medium in real time. This has the distinct advantage of direct transfer. Upon analysis with an oscilloscope or other equipment, the signal can be seen in its original form. However, high-end tape decks are not terribly portable. Portable units are notoriously noisy and suffer from a serious lack of fidelity. While I continue to use tape cassettes in many of my experiments, the tapes used are only of the metal type and I use a relatively good recording deck with a high quality head.

Technology will tend to advance, which has given rise to digital recorders. Whether done on optical disk, flash memory, or hard disk, digital recorders have undergone miniaturization many times over and are now just as portable as our cell phones, but what about quality? Quality of a digital recording comes down to two major factors: sampling rate and bandwidth. Sampling rate describes how many digital samples of the audio signal are taken every second. CDs are recorded at a rate of 44.1 kHz (44,100 samples per second) which has become somewhat of a standard for consumer audio. When speaking about other digital audio, such as MP3, sampling rate is replaced by data rate. Data rate with regards to MP3 files is the amount of data that is dedicated to the recording of audio every second. A typical MP3 data rate is 128 kB/sec which means that 128kb is used to create the file every second. Bandwidth is the frequency range of a recording. For example, human hearing ranges from about 20Hz to 20kHz, give or take. Ideally any recording will have at least this range of frequencies.

The sampling rate of a digital recording is mainly a function of the capability of the hardware used, and the higher the sampling rate, the higher the quality of the recording. According to the Nyquist Theory, the upper limit of a digital recording will be approximately half the sampling rate. Therefore, a recording made at 44.1kHz will top out at about 22kHz which is about 2kHz above the typical range of human hearing. This theory also claims that frequencies that are outside the range of human hearing will have an effect on those that are. For example, many audio enthusiasts claim that vinyl recordings sound better than digital. Vinyl records can produce frequencies at up to 50kHz, well outside the range of the human ear and so it is claimed that these high frequencies add to the quality of the recording as a whole. In the digital world, this would equate to a sampling rate of 96kHz producing an upper limit of 48kHz in the resultant recording. In general, for the purpose of later analysis the highest sampling rate is best.

Bandwidth, or frequency response, is a major quality consideration. For example, a CD recording has a frequency response that mimics that of human hearing while a telephone has a bandwidth of only about 3kHz. That means that in the case of a telephone conversation, only about 1/6^th of the frequencies we can hear are transmitted. All the rest is lost to the ether. Similar to sampling rate, larger bandwidth means a better recording. Let’s take a look at a couple of digital technologies as a function of these factors and see what might work best.

Optical disc recorders

Included in this category would be Minisic and other similar devices. While not always the most convenient, these units have a wide frequency response (20Hz to 20kHz) and CD quality (44.1kHz) sampling rates. Additionally, a single disc can store up to hours of audio. With an external high-quality microphone, these produce phenomenal recordings with very little background noise. I have used Minidisc for a number of years in conjunction with magnetic tape with wonderful results. On the downside though, the acquisition of the data to PC can be a bit cumbersome and using an external microphone is not always an optimal situation from a standpoint of portability.

Handheld digital voice recorders

These are among the most portable and convenient of devices available. They allow the capability to record almost anywhere, and most current units are equipped with USB interfaces to allow quick downloads of recorded data to a computer. Sounds great, right? Before we decide to go out and buy one, let’s take a look at the specs of some of these units. Most of the handheld voice recorders available at ‘big-box’ retailers are mediocre at best and unfortunately, these are what I see many investigators using. For instance, the Sony ICD-BM1A (a $300 unit) has a maximum sampling rate of only 16kHz, less than half that of Minidisc. Its frequency response is 60Hz to 13.5kHz, much narrower than that of the range of the human ear. So, while it is more convenient, that convenience comes with the cost of reduced quality. Olympus does produce a digital recorder with a sampling rate of 44.1kHz (CD quality), but with a reduced frequency response as well.

However, not all is lost for the handheld digital recorder. Once we step outside of the product offerings of the ‘big-box’ stores, we will find that many more options are available. For instance, the Zoom H2 and H4 provide phenomenal recording (up to 98kHz sampling in .wav format) and many additional features that the mainstream recorders can’t even approach. These types of professional level recorders would be a much better option for anyone with the desire to truly capture high-quality recordings and maintain ease of use and portability.

The final word

It seems that many groups are content to simply record audio than record high-quality audio that will stand up to serious analysis. This begs the question: are these investigators really trying to find out the origins of voices, or are the voices themselves enough? Whatever the purpose, we always need to make sure that the equipment we employ is commensurate with the duty it is to perform. If every effort is made to capture the best data possible, the skeptics may someday run out of arguments.

Thanks for taking the time.