Just got my Digi pre .....and guess what?

[mesh]

Hi All,

I just got my DIGI pre after waiting for quite some time, and with some shock and horror, I find when changing the gain (which only has 70 increments) there is a clicking sound (you can here a relay or something on each step). On the PT input meter, the click meters about a third of the scale.

What do you think about that?

I called my dealer, who gave me his first one, and rekons it might be faulty.

The other interesting thing is...you know those 8 rows of meters, they are not meters, that are status indicators for things like phantom and pads, the is one switchable (nice and big) meter for level. This means you can only meter one channel at a time from the box.

now the sound.....not sure yet, need more time.

mesh

[Digi-Slime-NYC]

Just wait until your tracking a singer (one side of her headphones off) with PRE and a weird bizarre midi message gets sent to the PRE and boosts the gain by +40 db, then your computer freezes. OUCH!!! you'll have many ears ringing. Be careful!

[pmklein]

Originally posted by Digi-Slime-NYC:
Just wait until your tracking a singer (one side of her headphones off) with PRE and a weird bizarre midi message gets sent to the PRE and boosts the gain by +40 db, then your computer freezes. OUCH!!! you'll have many ears ringing. Be careful!

<font size="2" face="Verdana, Arial">That's funny! Because it's a real possibility!

[Cauldronics]

Originally posted by pmklein:
<blockquote><font size="1" face="Verdana, Arial">quote:<hr /><font size="2" face="Verdana, Arial">Originally posted by Digi-Slime-NYC:
Just wait until your tracking a singer (one side of her headphones off) with PRE and a weird bizarre midi message gets sent to the PRE and boosts the gain by +40 db, then your computer freezes. OUCH!!! you'll have many ears ringing. Be careful!

<font size="2" face="Verdana, Arial">That's funny! Because it's a real possibility!<hr /></blockquote><font size="2" face="Verdana, Arial">Why did you buy this thing? Sounds like a nightmare.

[Stan Cotey]

Regarding the clicks heard while changing the gain on PRE, I thought I'd take a moment to explain what's going on and why these clicks occur. First though, the clicks are a normal and necessary result of the high-quality gain control method used in PRE. The highest priority item for us with PRE was the sonic quality and we worked hard to obtain the performance with the initial design and keep it there through the remote control process.

As some of you know, PRE is a precision, transformer-less design, and uses a high-precision differential transistor pair (actually, a bunch on 'em in parallel to reduce noise) as a front end in place of the traditional input transformer.

The gain control method used in PRE utilizes relays to place fixed resistors in the feedback path. To vary the gain of the circuit, you cross-couple some feedback from one side of the input to the other. There are very slight DC offsets present across these resistors.

When you change gains, some of the DC offset from one side of the circuit is injected into the other side and we get what is called a "step change". Basically, this comes out as a small transient or 'click'. There are plenty of non-remotely controlled mic preamps that utilize a variation of this type of design and they use a potentiometer for gain control, in which case the step change never occurs. On some of these preamps, you can quickly rotate the gain control and hear a "whoosh" or a scratching sound (depending on the type of pot used,) which is really the same artifact in disguise.

As a manufacturer, the real problem comes in when you want to remotely vary the gain of one of these circuits. You can easily use a VCA (voltage controlled amplifier) or an MDAC (multiplying digital-to-analog converter,) which delivers the convenience and reduced artifacts of a pot but unfortunately impairs the fidelity and performance substantially. Remember, the audio performance of PRE in terms of noise and distortion is very, very good and due to the high-gain design and critical nature of the circuits, it's very easy to impair this excellent performance with a less-than-excellent gain control method.

When it comes right down to it, there are only two methods of remotely controlling a transformer-less mic preamp that I'm aware of.

The first might be using an actual servo motor to drive an actual pot. If you can get around the noise of the motor circuit leaking into the sensitive audio electronics, it's a workable solution. Unfortunately, servo motors cost serious money, as do motor drivers, as does the additional power supply required to run them, which would raise the price substantially, not to mention the fact that we would have to fit eight of them in the case and then deal with the extra heat, etc.

Then, you have reliability concerns since you now have an electro-mechanical assembly in a critical path. Topping that off, you now have to deal with the error of the pot, which means that unless you calibrate each pot to each mic preamp, you can't have reliable gain amounts, which in turn makes it hard to work in stereo. So the cost, size, complexity and heat all go up while the reliability and accuracy are reduced.

The other option is to use relays to switch fixed precision resistors in the circuit. The benefits are many; performance and sound quality are maintained, cost is kept reasonable, reliability is high and gain matching between channels is great. The downsides are simple but livable given the other options; you have fixed gain steps and there are small clicks when changing gain. Since most of the professional engineers I know rarely change the gain setting while recording, I believe it is a small price to pay for the increased sonic performance and benefit of being able to locate the preamp at the source.

Regards,

Stan Cotey
Product Manager

[Lee Blaske]

Thanks for a thorough explanation.

I know digital gain control is difficult in these high gain situations. I have a Metric Halo Mobile i/o as a portable rig that uses a digital pot for mic pre control. It's click free, but there are trade-offs (it has a higher than optimal noise level at high gain settings).

I am curious about the fears some have expressed regarding stray MIDI messages inadvertantly setting the device to high gain (especially for a performer wearing phones). Has that been addressed in the design? I would think that safety could have been built in by requiring a very specific MIDI message to change gain, i.e. a command or sequence of commands that would have little likelihood of occuring randomly.

Lee Blaske

[SmlTwnGuy]

Originally posted by mesh:
I find when changing the gain (which only has 70 increments)

<font size="2" face="Verdana, Arial">You say that like it's a limitation. Some very desired, expensive pre-amps only have 8. 70 is luxury! How many do you need?

[Paul Turpin]

Since most of the professional engineers I know rarely change the gain setting while recording

<font size="2" face="Verdana, Arial">Changing gain while recording happens all the time. Which only really means that the PRE won't get used for certain things - like vocals where you've got 10 minutes and need to keep even the "Rehearsal" take during which you need to find the perfect setting while the singer is laying down something that just might be the only time they do it well!

[Stan Cotey]

Point taken. This same gain step change would happen if you were using a Neve 1272 or 1073, or any preamp with fixed gain steps for that matter. In that case and as with all things, you'd have to decide if the particular sonic characteristics of a preamp were right for the job at hand and what the other tradeoffs might be. In your given case, you may well want to use a preamp with fully variable gain.

I'll still stick with my statement that most if not all of the engineers I know rarely change preamp gain settings while recording. I often set preamp gain slightly conservatively and use the gain available in the fader to make up for it. To me, being a responsible engineer often means not going for the last few dB in order to preserve a little extra headroom for the musician's "inspiration" factor.

Regards,

Stan

[mesh]

Hi,

I thought there must be some resitors involved , you can here something like a relay clicking. In regards to you comment about engineers not changing gain when recording, well I think quite a few people do adjust a bit as they go, if the first take is rocking. In a pefect world you would have enought headroom, but sometimes the singer really surpises you with a much hotter take.
I spose if I keep it, I will have to be conservative.
Also is seems weird having all this clicking going on, with people wearing headphones and all. I take you point about a neve only having a few steps.
In regards to the increments, it actually does not have 70, it goes up in steps of 3 , so is more like 20 something.

Not sure what to do....

mesh