by John Gatski
The TASCAM’s audio performance, ergonomics, features and ease of use is first rate. It has really good cardioid microphones and the A/D-D/A converters nicely capture a recording in all its 24-bit detail.
The DR-100 records audio onto removable SD (up to 2GB) and SDHC cards (up to 32GB). A track’s maximum file size (adjusted in the Setup menu) is 2GB. When recording, a track that exceeds 2GB will automatically start another track.
On the DR-100 playback of the dubbed track, using the Shure SRH-880 headphones, I was impressed with the TASCAM’s playback quality. The drum cymbals had nearly the same open character and separation as the song played through my high-end separates. Pretty good sounding headphone amp, as well, with plenty of gain to drive the AKG K701s.
The combination of its A/D and microphones brings out the detail from bottom to top — and really good imaging. After copying these big guitar recordings to a DVD-A and playing them through the Oppo/Benchmark DAC1 Pre, I again confirmed my initial impressions of the high-quality A/D.
Testing by Tom Mintner
Editor's Note: Thomas E. (Tom) Mintner has joined the Everything Audio Network with his test and measurement services, SpecCheck by Audio Support Northwest. A SpecCheck evaluation utilizes the extensive hardware and software test resources available at his lab, co-located near Portland, Oregon with his other company, NTI Americas Inc. NTI Americas is part of the worldwide NTi Audio partnership, which manufactures audio analyzers/generators, as well as PureSound production test solutions for factory production lines.
Although portable digital recorders and other small audio devices face a number of challenges at the design level, the TASCAM DR-100’s test results show a very clean recording capability. Technical challenges for this class of recorder/player are created because of limits on battery power consumption — as well as the related heat dissipation, PC board space, and other product package-size and functional issues.
For example, A/D and D/A converter chips often selected for use in mains-powered studio grade converter products, are generally too large and consume too much power, often at internal supply voltages not available in a mobile device. Sometimes, various combinations of switching-power supply and audio-path technologies for mobile devices combine in ways that can provide a fairly good numerical spec — but with “digital nasties” visible down near and above the average noise floor in a spectrum analysis of the signals.
It seems that the engineers at TASCAM took on these challenges and produced a design with not only excellent numerical specifications — but also clean, uniform noise floors and residual distortion characteristics.
The following commentary summarizes my findings during testing of the DR-100. I tested both the DR-100’s line inputs, which are on 1/8-inch (aka 3.5-mm) stereo phone jacks, and via the XLR connectors intended for external microphones.
Interestingly, the different audio paths measured nearly identical (once input levels and gains were figured in), except when the highest overall gain settings were used. The good results from either input is significant because I have seen some small recorders that don’t measure up when an external microphone is plugged into the microphone inputs, or when you need a little more gain. With critical use likely to come through external mics, the graphs represented in this bench test were obtained via the DR-100’s XLR connectors.
Given the positioning of this product, I felt that end-users would buy it more for its linear recording modes, and so I focused my measurements within those parameters. Starting with the basics, the DR-100‘s frequency response, I took readings at the three sampling rates 44.1 kHz, 48 kHz and 96 kHz (Figure 1); the measurement graphs were scaled to illustrate the well-behaved HF roll off tails as the signals approach the frequency limits of each rate.
To better judge the response “flatness” and response matching between channels, Figure 2 shows the response within only a 20 kHz range and with a greatly expanded vertical scale. Also the second channel was deliberately offset manually to allow an easier “eyeball” comparison of the uniformity of response between the two channels.
The other important area to note is the relatively low deviations or response ripple towards the top end — where the system would begin to naturally roll off. Of course at each higher sample rate (48 kHz or 96 kHz), the response extends much farther beyond 20 kHz, as shown in Figure 3.
Figures 4 and 5 show the results of two less-conventional tests. Figure 4 is a spectrum analysis of the residual noise and distortion left when a high-level standard single tone signal is recorded on the DR-100 — with the original signal fundamental removed prior to the FFT analysis. This measurement was then repeated and averaged, which makes coherent discrete signals emerge visually on the graph and lowers the relative visual level of any regular noise, which is non-coherent.
Aside from some expected harmonic distortion at very reasonable levels the only other noticeable artifacts I could see were a bit of power line harmonics. Since I was running the DR-100 on its included external AC-to-DC supply, these hum components could have been related to the wall power.
A second test was run using a synchronous multi-tone of very wide bandwidth and high level. Sine testing and standard THD+N measurements always provide some useful and irreplaceable reference comparison points for almost any audio testing. But we all know that music does not usually consist only (with homage paid to David Tudor and John Cage) of single pure sine waves. Multi-tones are somewhat more music-like collections of sine waves — with known phase, amplitude and frequency characteristics. These test signals are chosen so that the entire signal may be presented at a level that is tolerable to a device under test — without causing clipping or overload due to crest factor.
In essence, multi-tone signals are a form of wide-band “stress test” for an audio device. Figure 5 shows the DR-100 with a wideband, equal amplitude, multi-tone test signal. Such a signal is not bandwidth-shaped like a true music simulation would be, but provides a difficult test for any digital device that might exhibit non-linearity with complex input signals. The comb-like trace is the multi-tone signal itself.
With digital audio devices, I am interested in the “cleanliness” of spaces in-between the “tines” of the comb. The stuff spaced down in between the many multi-tone components is where noise, distortion, and, in particular, any “birdies” or other digital-related “trash” would appear.
Try this test on a device using any of the popular reduced bit rate codecs, and the bin spaces between the tones fill gradually with audio “debris.” However, the importance and audibility of that debris is then subject to mitigation due to the masking phenomenon, such that much of it is inaudible in the presence of the nearby program frequencies. With its linear recording design, it is comforting that we don’t have to worry about the reduced-bit audio debris clutter in the DR-100‘s measurements.
I also ran a standard signal-to-noise test on the DR-100, and the result as expected varied slightly — depending upon what maximum reference level is input to the device; which device input is used; and the gain setting. But the average signal-to noise ratio was always better than 90 dB, typically 93 to 99 dB. I also made a sweep, measuring THD+N at many frequency points, within a 22 kHz measuring bandwidth. The extremely respectable noise distortion performance of the DR-100 can be seen in Figure 6.
Since this is still primarily a field recorder, it offers selectable stages of low-frequency roll-off filtering for recording. These High Pass (HP) filters could be used for either speech-only recordings, or even for music recording in a venue with, say, typical HVAC low-frequency room rumble. Figure 7 shows the low-frequency response of the DR-100 for each of the available low-cut filters.
Tom Mintner’s career/professional training spans both music and audio engineering, starting with his first professional experience when conductor Henry Mazer first tapped him as a substitute orchestral clarinetist at the age of 16. His formal training at Northwestern University included both Music and Physics and his informal training included jazz, electronic music and commercial recording work in nearby Chicago. He then was appointed a Rockefeller Foundation sponsored Performer/Fellow and Audio Specialist in the Center for New Performing Arts at The University of Iowa.
Joining Rupert Neve Inc., He began a 30+ year career directly in the professional audio equipment sector. Working in New York and then Nashville with Neve and then Studer ReVox, he has held a variety of senior level technical, sales and management positions. Before founding NTI Americas he was a long-time key employee and part owner of audio test & measurement company Audio Precision. He also developed semi-conductor ATE instruments for Credence Systems. He is a voting member of NARAS, and a member of the Audio Engineering Society, the Acoustical Society of America and IEEE.
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