MRC01
Major Contributor
For the past 15 years I've had an old Zoom H4 recorder and it's served me well as a portable preamp for my Rode NT1A mics. Back when I first got it, I did a simple mod to improve its sound quality. Lately it's been getting glitchy & buggy. It will suddenly shut itself off when attempting to give the mics 48 V phantom power. It will occasionally drop signal or freeze when used as a USB audio interface. I liked the Tascam 300 that Amir reviewed, especially its high quality mic preamps. But the 300 doesn't have a USB audio interface. I need this since I'm using those Rode mics for conference calls on my PC. So I bought a Tascam 40X to replace my old H4. Knowing its mic preamps are not as good as those on the 300, I wondered "how bad are they?" so I took a few simple measurements.
The Tascam 40X costs about $170. It has built-in mics and has connectors for balanced inputs, both 1/4" TRS and XLR. These inputs accept line-level and low (microphone) level inputs. It can give external mics phantom power at 48 or 24 V. It is a standalone recorder that runs on 3 AA batteries and uses an SD card. It has a USB connector that can be used for file transfer, or for a live audio interface (something the Tascam 300 does not support). In the latter mode it can use the built-in mics, or external mics. For example, with my Rode NT1A mics, the 40X will give them 48 V phantom power and I can use it as a mic preamp and A/D converter, connect it to my PC over USB, and it shows up as an audio device with a digital input having the live mic feed. The Tascam has a bunch of other features, like multi-track recording, etc.
I measured FR and HD with REW using my Juli@ sound card in balanced mode, connecting to the Tascam's 1/4" analog TRS inputs, and having the Tascam record the sweeps to its internal SD card. Then I copied those files the Tascam created to my PC and used REW to "import sweep" comparing it against REW's original sweep file. I measured it this way because that's how I'd use it in the field. These measurements should reveal the 40X mic preamp and A/D converter quality. That is, any flaws or deviations would be either in its mic preamp A/D converter. In each graph, the black line is the Juli@ loopback, which is my reference since that's what sent the analog signal to the Tascam. Green is right, Red is left (like a boat or airplane). Here are the results.
Frequency response at 96-24. Here you can see the wiggles come from the Juli@ I used to measure, not from the Tascam. The Tascam has some slight bass rolloff, but not much as the scale is 1/10 dB. Bass is down about 0.5 dB @ 20 Hz which should be immaterial. The Tascam's right channel is about 0.08 dB quieter than the left.
Frequency response at 44-16. Similar to 96-24 with bass rolloff and channel imbalance, though the Tascam rolls off a touch early in the high frequencies.
Let's zoom in on that top octave to get a better idea what's happening. The Tascam is down about -1 dB at 20 kHz. In my view, -1 dB @ 20 kHz is immaterial. But if you don't like that, it's a limitation of the A/D converter, not of the mic preamp. You can always sample at 48k or 96k to get ruler flat response well beyond 20 kHz.
Now let's look at harmonic distortion. Here's the Juli@ in loopback mode at 96-24. THD varies from -90 to -100 dB through the spectrum. This is nowhere near SOTA but it's not bad for a PC sound card that was already a few years old when I bought it over 6 years ago. The Juli@'s distortion at 44-16 is virtually the same so I won't bother to put up the graph.
Here's the Tascam 40X distortion at 96-24. It's about 10 dB higher than the Juli@ through the critical spectrum where our hearing is most sensitive to distortion. This should be well below audible thresholds, most likely lower than even very high quality external microphones you might connect to this recorder.
Overall, the Tascam 40X looks decent for a pocket recorder. Its mic preamps are not as clean as the 300, but it does everything I need to replace my old H4 and has no obvious problems in measurements. I'm happy to send this unit to @amirm for more detailed measurements, if anyone is interested in that.
The Tascam 40X costs about $170. It has built-in mics and has connectors for balanced inputs, both 1/4" TRS and XLR. These inputs accept line-level and low (microphone) level inputs. It can give external mics phantom power at 48 or 24 V. It is a standalone recorder that runs on 3 AA batteries and uses an SD card. It has a USB connector that can be used for file transfer, or for a live audio interface (something the Tascam 300 does not support). In the latter mode it can use the built-in mics, or external mics. For example, with my Rode NT1A mics, the 40X will give them 48 V phantom power and I can use it as a mic preamp and A/D converter, connect it to my PC over USB, and it shows up as an audio device with a digital input having the live mic feed. The Tascam has a bunch of other features, like multi-track recording, etc.
I measured FR and HD with REW using my Juli@ sound card in balanced mode, connecting to the Tascam's 1/4" analog TRS inputs, and having the Tascam record the sweeps to its internal SD card. Then I copied those files the Tascam created to my PC and used REW to "import sweep" comparing it against REW's original sweep file. I measured it this way because that's how I'd use it in the field. These measurements should reveal the 40X mic preamp and A/D converter quality. That is, any flaws or deviations would be either in its mic preamp A/D converter. In each graph, the black line is the Juli@ loopback, which is my reference since that's what sent the analog signal to the Tascam. Green is right, Red is left (like a boat or airplane). Here are the results.
Frequency response at 96-24. Here you can see the wiggles come from the Juli@ I used to measure, not from the Tascam. The Tascam has some slight bass rolloff, but not much as the scale is 1/10 dB. Bass is down about 0.5 dB @ 20 Hz which should be immaterial. The Tascam's right channel is about 0.08 dB quieter than the left.
Frequency response at 44-16. Similar to 96-24 with bass rolloff and channel imbalance, though the Tascam rolls off a touch early in the high frequencies.
Let's zoom in on that top octave to get a better idea what's happening. The Tascam is down about -1 dB at 20 kHz. In my view, -1 dB @ 20 kHz is immaterial. But if you don't like that, it's a limitation of the A/D converter, not of the mic preamp. You can always sample at 48k or 96k to get ruler flat response well beyond 20 kHz.
Now let's look at harmonic distortion. Here's the Juli@ in loopback mode at 96-24. THD varies from -90 to -100 dB through the spectrum. This is nowhere near SOTA but it's not bad for a PC sound card that was already a few years old when I bought it over 6 years ago. The Juli@'s distortion at 44-16 is virtually the same so I won't bother to put up the graph.
Here's the Tascam 40X distortion at 96-24. It's about 10 dB higher than the Juli@ through the critical spectrum where our hearing is most sensitive to distortion. This should be well below audible thresholds, most likely lower than even very high quality external microphones you might connect to this recorder.
Overall, the Tascam 40X looks decent for a pocket recorder. Its mic preamps are not as clean as the 300, but it does everything I need to replace my old H4 and has no obvious problems in measurements. I'm happy to send this unit to @amirm for more detailed measurements, if anyone is interested in that.
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The A/D side I am sure would still be quite capable by modern standards, if perhaps with a few mods (there have been plenty, but people generally didn't verify their effect properly).