Newbie Question - Do I need an external ADC?

Hello everyone,

I am about to start a new project of digitizing my entire record collection of about 400 albums, using audacity. I am new to the whole world of digital music and using Audacity, but I have been doing some reading of some online articles about the subject.

My setup is as follows: a Pro-Ject turntable connected to a Pro-Ject Tube phono preamp (Pro-Ject Tube Box S) , which is then connected directly into the line in of my Mac Pro. As you can see it is all analog until it reaches inside of the Mac Pro. After reading some articles and studying the LP digital workflow article here, I want to save each recording initially as a master recording probably in WAV format at either 48 or 96 kHz and using a depth of 32 float. Hard disk space is not a problem, and as I said these will be master files that I will reduce down eventually depending on what I need them for, either iTunes in ALAC, general FLAC or perhaps high-end audio 96/24 FLAC.

I thought all I had to do was set the quality preferences in Audacity to do this but I’ve since discovered that the maximum settings on the audio MIDI panel are 96/24 (in the Utilities folder), and I would like at least 96/32 bit float.

So my question is do I need an external ADC that will do 32-bit float and if so which ones can you recommend, … looking to spend between 200 to $1000 if necessary,


is there something I’m missing somewhere in the software settings that will allow me to do this?

What I don’t want to do is to record in 96/24 and have Audacity pad it up to 96/32 or even 96/32 bit float. I want to record in real 32-bit float if possible.

Thanks for reading,


That may be the limit inside the Mac. The ADC is very, very, good, but it’s not God’s Gift. They assume if you’re going to go completely nuts, you’ll do it outside the computer.

There is a very good, high end preamp with USB output, and the other elves will tell you what it is.

I don’t record that high a quality, so it never came up for me.


State of the art audio ADCs are up to 24 bit (of which the lsb is garbage).
Top of the range professional studio ADCs are “only” 24 bit.

I think Koz is referring to the ARTcessories USB Phono Plus - see:

For my LP digibitting I run an ARTcessories USB-DJ-Pre11 (which is basically just the phono pre-amp part of the USB Phon Plus - but without the USB services) - I than run this into an external USB soundacrd (Edirol UA-1EX - no longer available). If the integrated ART device had been available when I was making my purchasing decision I almost certainly would have bought it.


Thanks kozikowski:

Upon further investigation you are right! From the “Audio MIDI Setup” app in the Utility folder, you can select the sample rate and bit depth for the “Line in”.

What is curious is that for my MacBook Pro (mid 2010), I can choose 32bit Float for the bit depth of the line in; hoverer for my MacPro (also mid 2010) I can only choose up to 24bit Integer for the bit depth of the line in.

The only difference in terms of Audio between the the machines is that the MacBook Pro has “Intel High Definition Audio: Audio ID 71” and the MacPro has "Intel High Definition Audio: Audio ID: 66".

It’s a bit strange since a 32-bit float will create much larger file sizes and the MacBook Pro is limited to one internal hard drive whereas the Mac Pro has four drive bays for 3 1/2 inch drives up to 3 TB each.

Initially I had thought that the program Audacity would perform the ADC functions via its own software or a plug-in. I guess I was wrong (as I say I’m still a newbie about this).

I realize 24-bit is more than acceptable and used by professionals and audiophiles and that will be what I will exporting for the final versions to be listened to. The only reason I’m interested in saving the master files is 32 bit float is that you would retain the maximum amount of information per sample. I got this from two sources the first book audacity by Carla Schroder and second from the tutorial posted online here “Sample workflow for LP digitalization” which says in part quote:

"Raw master backup

“Export a single WAV for this side of the LP at 32-bit float (not 16-bit). Retain this WAV file as a maximum quality “raw-capture” file that you can import back in to Audacity later for any future re-editing (or to start over with editing if you damage the project while working on it).”



The ADC will not actually be converting with 32 bit float precision. At best it will be capable of a maximum of 22 bit precision. Bit formats can be converted to higher bit formats losslessly, so for example an ADC could theoretically convert the analogue signal to 16 bit integer format and then output that data as 128 bit float (though that would be pointless because it is still really only 16 bit precision.)

Audacity can convert the bit format internally. So for example if the ADC sends 24 bit data to Audacity and Audacity is set to record in 32 bit float (default) then Audacity will put the data into a 32 bit float audio track and convert (losslessly) to 32 bit float format when required.

32 bit float is generally recommended as the recording bit depth in Audacity because processing can be done more efficiently and with greater precision,

If the recorded audio data is say 16 bit, then there are 65536 possible values for each sample (16777216 possible values for 24 bit). If you amplify (or process in any other way) that 16 bit data, some of the samples may need to take values that lie between the available digits. If the track is set to 16 bit, then those values would need to be rounded to one of the available 16 bit values. On the other hand, 32 bit float can accommodate fractional values that lie between 16 bit (or 24 bit) values and so provide a much more accurate result. Exporting your master recoding as a 32-bit float WAV file allows you to retain this extreme precision.

When converting from a high bit depth (such as 32 bit float) to a lower bit depth (such as 16 bit integer), some sample values may need to be rounded to an available value, causing some loss of precision.


I wrote that workflow tutorial and I stand by that advice :sunglasses:

My workflow actually involves the 32-bit raw master doing double-duty: I export the raw master and then pass it throgh Brian Davies’ excellent ClickRepair software and then feed the repaired 32-bit WAV back into Audacity (CR is non-destructive as it creates a repaired copy). See this sticky thread: Click/pop removal - ClickRepair software


Well the ASIO driver on my Asus Xonar D2 card has a 32bit setting, but I’m fairly sure the ADC is 24bit and I assume the card is just upsampling that somehow.

However, isn’t this bit depth discussion a bit of a red herring?

I don’t actually have the slightest idea what a ‘Mac Pro’ is, but by the sounds of things the OP is intending to use its onboard soundcard. Given that he seemingly has a fairly high end hi-fi setup, isn’t he likely to get some - perhaps significant - improvement by buying an external soundcard, if only a cheap one to get the ADC out of the way of electrical interference and ‘noise’ inside the box?

a cheap one to get the ADC out of the way of electrical interference and ‘noise’ inside the box?

We don’t have noise. I do broadcast sound recording sessions with the Stereo Line-In on my MacBook Pro.

It’s one of the things we got when we paid “all that extra money” that the Windows people keep poking fun at us for spending.


I think I see where you’re coming from; the audio processing circuitry is actually physically protected by the reality distortion field! :smiley:

Anyway, my intention is not to engage in Apple flaming but rather to help identify a possible replacement for my own Asus Xonar soundcard, which being non-magical must resort to a metal case shielding it from electrical interference, and is the PCI version allowing it to be seated as far away from the video card as possible.

But the problem is I need to replace my computer soon, likely with the next Intel version out next year, and PCI seems to be a technology firmly on the endangered species list. Several reports now suggest PCI will finally go the way of the Dodo in the new Intel architecture, so I am interested in suggestions for replacements of comparable quality. Anybody?

protected by the reality distortion field!

Or more likely, the superior, extra-cost cabinet shielding. The distortion field is needed when you write the check.

There is another trend in PCs. People recording entertainment content (trust me, the way I do it, it’s “content” not music) on Windows machines discover that they’re not general purpose computers any more. Microsoft threw it’s lot in with Corporate Interests and the machines come out of the shrink wrap set for conferencing, communications, and collaboration, not recording arpeggios.

It would appear that external sound devices (USB3??) are normal, not the expensive, exotic exception. You could always get an internal “Sound Card” that had Superior Shielding, XLR connectors and good microphone amplifiers. Few people bought them, but you could. Now, you can’t.

Sound On Sound magazine regularly does equipment reviews and the local news stand carries it. I buy the ones that review the stuff I’m interested in. I think the latest one I have was microphone amplifiers.