In this review, I’ll be comparing two channel strips from Presonus, the Eureka
The Eureka
What is a Studio Channel Strip?
Well, it’s not Lady Gaga taking her clothes off at a distributers launch meeting, unfortunately. It’s a single channel of the stuff that used to go into a mixing console back in the days.
Typically, when you work with a studio console you’ll want the flexibility to sculpture the sound you put on tape – and an experienced engineer knows that a take nailed is a day saved in preparing for the mix.
It takes 3 minutes to record a part, and it may take forever fiddling about with effects afterwards.
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| Rupert Neve designed some much sought after consoles The technical design was much inferior to the Eureka, but they coloured the sound in a nice way, and made the tracks "sit" well in the mix. |
So when time is tight you tend to record the actual sound you want – or as close as you can manage. In this way, only polishing is needed afterwards, and this makes both the artist and the engineer focus on the actual artistic performance, because everybody hears what a part will sound like when its done.
It takes lots of engineering skills and even more experience to sculpt a basic sound at the tracking stage. With the advent of DAWs, focus has changed to the endless sculpting possibilities offered by plugins and emulators and simulators and fancy editing. “We’ll fix it in the mix” has become the standard reply to any expressed doubt about a tracks sonic qualities at take time, making engineers spend endless hours trying to design something after the fact that should have been “in the can” by the time the artist left.
Therefore, bying a Channel Strip is a step back to the good old days of basic sound sculpting at the tracking stage. To do basic sound sculpting you need to control the dynamics, the tonal balance and the time element of the performance there and then.
These two offerings from Presonus include a mic and instrument pre-amp with adjustable “phatness” - a general purpose compressor for dynamics and a three band EQ to sculpt the tone. The Eureka
Two units can hook up to share the optional digital I/O board. A pair of Eurekas and a Lexicon MX300 would make a great retro stereo tracking console to speed up DAW workflow.
But we’re getting ahead of ourselves. In order for any of this to make sense, the units themselves must be able to perform reliably to a high standard, and the features must actually work. Otherwise you'll just trade DAW frustration for Channel strip fatigue!
What do they sound like?
I first listened carefully to the unit using both condenser and dynamic microphones. I tried playing back recorded material through both units. I fiddled with the knobs. I played around. Here’s what I found.
The Studio Sound:
This unit sounds hard and forward, and noisy. It's actually pretty annoying on a condenser mic – suggesting that the input stage prefers a low impedance.
The design is such that the gain leaps up when the gain control is cranked all the way, and the unit really sounds terrible at its highest gain setting.
On a dynamic mic with a normal studio signal level – when mic’ing a vocal performance or an instrument - the unit fares better, delivering an acceptable performance. On any sort of transient material, like cymbals, plucked western guitar, percussion, it simply borders on the unusable. It makes your WAV-files sound like MP3’s. It’s that hard. Gritty is not an overstatement of the nature of it’s sound.
The pre amp design is extremely sensitive to the impedance seen on its input terminals. A 220 Ohm load gives an excellent noise floor of –96dB at allmost full gain. . This is marred by two factors. Firstly, turning the gain knob one notch up, brings the whole amp to its knees with hum and power supply components at only –54 dB, and unacceptable distortion specs. Without the tube drive active, things are about 10dB better hum wise, and 6dB better noise wise.
For a condenser microphone, the situation is worse, with a noise floor of only –84dB. This means that if you're used to adding a bit of treble boost to vocals and using a compressor to make them stand out, you'll not be able to do this without getting an unacceptable noisy track. In this day and age this is just not accaptable performance. I made the mistake of using this unit to track a female singer in an actual production setting, and had to spend hours trying to mask the noise on her vocal track. On the record you can still hear the hiss as the instruments fade out towards the end of the track leaving the vocal all on its own - centre stage.
The Eureka Experience
It is hard to imagine that these two units come from the same manufacturer. This pre-amp is clean sounding. Strings have “air”, violins and acoustic guitar sounds present and “open”, and percussion sounds well paced.
The input impedance switch is nice for taming cheap dynamic mics, and can even flatter the sound of an SM57 when set to 50 Ohms. This is much of a taste issue, but it’s nice to be given the option.
And yes, the knob does make a difference.
The noise quality is that of silken smooth hiss, The input stage uses a transformer, thus limiting its ultimate clarity, but adding definite benefits in terms of common mode rejection. The straight dope on this is that the Eureka
Turn my knob and see what happens..
Both units feature a knob that adds variable amounts of distortion to the recorded signal. This is variously describes as adding “phatness”, warmth or an “analogue” sound.
The hype is bewildering, and I’ve even read that this feature gives recordings “tape warmth!”
This is bullshit of course, as the distortion mechanism of tape is vastly different from that of a FET or a tube.
Both knobs add about 1% of even and odd harmonics to the signal, mostly 2nd with a nice tapering off as we go up the harmonic scale. The Studio Channel offers this feature on all of its inputs, whereas the Eureka
The Studio Channel really injects an asymmetric clipping type of distortion, not a natural “tube” sound that you would get from a tube circuit without global feedback. So it has more in common with a slightly overdriven guitar amp than a good piece of tube gear from yesterday.
Would you want a female vocal recorded through your Fender Twin? Well, it won’t sit well in the mix or blend easily with backing vocals if you do. In fact, you’ll have a hard time making it blend in with anything.
But give me a male singer who lacks a bit of grit, and it may be just the ticket.
On bass guitar it adds definition, but on anything complicated it just adds muddiness. A player picking his quality western guitar goes from sounding open and clear to compacted and solid – in effect you’re knocking a few zeros off of the perceived price of the instrument.
Is this desirable or even useful?
"In the box" I use exiters and tube warmers. They alter the sound in quite different ways than this effect. Or the good ones do. Bad ones work just like the Studio Channel in that they add both even and odd harmonics, and that just muddies things. And the distortion doesn't vary with level like the real thing.
These effects are supposed to mimic a valve preamp, I presume. For vintage phatness, a real vintage box adds second harmonic distortion and an touch of fourth order distortion, along with a tad compression. This gently squishes the signal adding about half a percent distortion total in the process. With the Presonus Studio Channel there is no squish and no gentleness, you just get a dose of full blown Fender Twin Reverb at all levels, making for an unnatural effect.
The Eureka Eureka 9 o’clock setting – it will be too subtle a change.
For nice things to happen at all, you need a hot input signal. The more gain you dial in, the less distortion there will be. The effect is directly proportional to the input signal level, NOT the output signal level.
So for a max tube experience, set “saturate” to maximum, gain to minimum, and drive the input until the “clip” LED lights up on peaks.
You’ll get a maximum of 4% 2nd harmonic distortion when applying a line level (+4dBu) signal to the mic or instrument inputs.
So summing up – you will have to drive the Eureka
As an interesting aside – the noise floor drops about 6dB when the valve emulation is on, thus confirming that FET current noise is a major contributor to front end noise performance. The gain also drops slightly, by 1 db, but the extra 5dB S/N improvement may come in handy with low output ribbon microphones.
Hum is comfortably low at –86dB and the noise floor is close to -110 dB at best, and –81 and -98dB respectively at max gain. The EQ section adds very little noise. The noise is independent of the source impedance or the connection of a normal microphone cable.
The Studio Channel on the other hand, picks up noise from leads easily, and needs to be plugged into something to be reasonably quiet. This is the main reason transformers are used in traditional studio gear.
Noise modulation
One reason why gear sound bad is because of noise modulation effects. Noise present in the system – often from a badly designed power supply – is mixed with the signal in a non-linear fashion, and you get AM and FM sidebands making the music all wobbly to your ears.
There is a marked difference in the two units when it comes to noise performance – The Eureka has a well designed, and hence quiet, power supply, whereas the Studio Channel suffers from quite noticeable modulation effects.
These effects are most pronounced in the midrange frequency band, and colours the sound making it forward and bright. It also makes the noise sound aggressive, whereas the Eureka
The parametric EQ
Both units come with a three band parametric equalizer, but the similarity stops there.
The Studio Channel features a bass and treble section that work as shelving filters giving appx +- 10dB of boos or cut, or as peaking filters giving an extra 2 db in the boost department.
The “Q” or sharpness of these two “peaking” filters is such that they do not lend themselves to surgical EQ, they are really only bass and treble controls that can sound smooth (shelving) or quite obvious (peak). So in a real life situation, you only have 1 band of parametric EQ, sweepable from 250Hz to 2,5kHz. A very usefull range, and often that's enough at the tracking stage. Let's face it, if a source needs three bands of EQ that bad, you'll probably want to re-position a mic or two!
The bass and treble sections sound ok when used in shelving mode and with moderation. But they affect the sound so much that you would rarely want to use them at their extreme settings.
The Eurekas features a “real” three band parametric equaliser with adjustable gain, frequency and “Q” for all three bands.
It’s worth noting that the Eureka, because of its transformer input, may sound a bit thin in the deep bass region, being –3dB at 30Hz. The flattest frequency response was obtained with the “Saturation” control in the 3 o’clock position, when the response is ruler straight down to 50Hz..
Without the help of the saturation control, a flat response down to 50Hz can be had by giving 1 click of boost at the lowest frequency. This makes quite a difference to the sound of the unit.
The controls are quite sensitive around their centre position, the indicated centre resulted in a 1db boost in the treble. So for this unit, a +1 click in the bass and a –1 click in the treble provided a flat response. The midrange band semed to be ok calibrated.
This is an important omission from Presonus. A total of close to 2dB imbalance between the top and bottom of the frequency range is readily audible, and will lead to the unit getting a reputation for sounding “thin” when using the EQ.
Even a cheap Mackie mixer, as well as the much simpler Studio Channel, has this aspect covered.
The bass EQ of the Eureka gives you roughly 10dB of boost and 12 dB of cut, and with the Q set to it’s lowest setting, approximates the Studio Channels EQ in peak mode. The frequency calibration is a bit off, 100Hz indicated equalling 150Hz.
The bass EQ frequency can be adjusted from 50 to 350 Hz, with a high Q setting offering a nice “surgical” cut or boost in the difficult boom region around 200Hz.
The midrange control extends from 250Hz to 3,5kHz. The filter curves were not as symmetrical as DAW user are used to seeing, being based on physical filters with the usual design constraints.. There is no serious band interaction between the filters, and they sound quite musical. That means it’s possible to boost in the region from 5-10Khz to make a vocal “breathe” without it sounding sibilant or harsh.
The rumble filter cuts –3dB at 80Hz.as promised, and rolls gently off with little ringing.
If you want the most pleasing treble lift, set the treble band to 6,5kHz and the “Q” to minimum, and apply a gentle boost (between 1 and 2 o’clock). This will give you an approximate shelving curve centering on 10kHz with a 4dB lift. This results in very little transient distortion, whereas full peak boost at 18kHz results in a bright sound.
The dynamics section
The compressor in the Eureka
All the usual controls are there, including a high pass filter for the control voltage to the sidechain making it possible to use the compressor as a de-esser, and to avoid distortion when using fast attack times by not processing the lower frequencies. This is not a moot point, as the Eureka
The attack and release curves were nice and symmetrical on the Eureka
Both compressors offer a maximum of 2:1 compression. That means that for signals above the threshold, a 10 db increase in input level results in a 5dB increase in output level. I have seen many say that these compressors have a greater compression ratio – but my values are based on measurements So no matter what the internet says: do your own math! (It is embarrassing that Sound On Sound reviewer Hugh Robjohns states that the Eurekas compressor can be set up as a limiter. I wonder exactly how that is to be accomplished?)
2:1 is not aggressive compression by any means, but a useful addition to be used during tracking to control dynamics.
What would be even better was to have a built in brick wall limiter to stop the A/D converter from clipping the signal, but that they ain’t got!
Summing up
Both units offer enough features to make any tracking engineer happy. But whereas the Eureka holds good on its promises and provides excellent performance in the studio as well as on the test bench, the Studio Channel does not.
The Eureka can handle any type of mic and deliver a clear, or a warm sound at the twist of a knob. The Studio Channel sounds its best with a dynamic mic without any tube distortion.
Both compressors offer decent performance, The Eureka again taking the lead with a more linear design and the ability to do slight sibilance correction.
The Studio Channel has a nice sounding EQ, that no doubt would have been more usefull if not let down by an overall noisy design.
If you want a good allround preamp that sounds as good as any mixing console regardless of price, go for the Eureka. It is clean, uncoloured and transparent.
If you're on a budget, and can't afford the Eureka, don't waste your money on the Studio Channel. It really DOES sound worse than a Behringer or Mackie mixer, so if you already have one of those, you're better off staying put while you save up for some decent gear!
Appendix - Measurements
The measurements and the subjective evaluation were in agreement.
The distortion measurements were done using both conventional distrortion measurement techniques, and also by using a three frequency test signal, allowing both intermodulation and harmonic distortion to be measured.
In adition, I also did 200 Hz harmonic distortion tests to check in the critical vocal area.
Here you see the Studio Channel harmonic distortion spectrum at full blast, without the tube. Predominantly second and third harmonic distortion, with noise modulation products in between.
The spectrum to the left shows the effect of the Studio Channel tube. Notice how we have both even and odd harmonics in what is basically a feedback amplifier clipping type spectrum.
The noise spectrum of the Studio Channel with a dynamic microphone. Notice the peaks at the mains frequency (50Hz, and all its even and odd harmonics. You can also make out intermodulation components.)
Compare the noise spectrum above with the noise spectrum of the Eureka under identical conditions.
You don't need to know much about audio engineering to notice that the noise is further down, and consists of a smooth hiss with slight intrusions from mains rectified (100Hz) hum.
And remember, this is in a studio setting with max gain, so it represents a real life recording situation.
The Eureka has commendable low distortion when used in its clean mode.
There is virtually no distortion appart from a slight 2nd harmonic component even at worst case conditions. (The peak at 400Hz.)
Very litle modulation noise and low mains hum.
With the distortion knob at full blast and its input driven hard, the Eureka does a good job of emulation a vintage valve piece of equipment:
This is reminiscent of a high quality valve amplifier of days gone bye.
When the volume is turned down, the valve simulation correctly greatly reduces 3.rd harmonic distortion, giving this pretty picture:
Here we see the correct way to do things, only a slight second harmonic component is left.
In fact, the valve gear it emulates is of such high quality that you would have a hard time hearing the typical "valve sound" at all.
There are some intermodulatyion componenmts, indicating that the preamp is colouring the sound and there will be some loss of clarity. Notice the +-50Hz components around the second harmonic peak at 400Hz.
The difference between a real parametric EQ and a "peaking EQ" is shown below.
First, let's look at the bass boost of the Eureka set to 100Hz and max boost:
Then compare it to the Studio Channel set to its peak mode:
There is nothing "surgical" about this boost. It just boosts everything in the bass region, much like an oldfashioned bass tone control.
Appendix 2 - Who is this guy anyway?
My name is Paal Rasmussen, and I used to work in the audio business. Back when there were no PC's and reviewers actually knew what they were talking about.
I was one such reviewer. My equipment reviews were published in various UK publications, including The Gramaphone, HiFi News, Audio, Popular HiFi and Audio, and HiFi for Pleasure.
I consulted for some minor and major audio companies, and designed a few loudspeakers - I was at one time employed by SEAS Høyttalerfabrikk where I made the first prototype rigid cone loudspeaker drive unit.
I later joined the Norwegian HiFi manufacturer ”Electrocompaniet” – where I was responsible for testing, and moved on to form Sandstrøm AS and The Norwegian Radio Mfg. Co. – NRF for short. We designed, developed and produced some highly acclaimed audio gear including a modified version of Matti Otala’s TIM-free power amplifier, as well as high power amplifiers, tape recorder electronics and much other besides.
I have also worked as a recording engineer, and producer. In my spare time I even play some musical instruments. 