I typically record vinyl using an external ADC with its own input gain control. I leave Audacity recording level at 100% and use the ADC controls to set recording levels. Now, I’ve run into a situation where recording is being done from a 16/44 USB turntable with no gain control. Setting recording levels is accomplished using Audacity’s recording level slider typically set near to 70%. I’d like to understand what trade-offs exist when using the recording level slider in Audacity rather than controling volume externally. I’ve read that digital volume works by truncating bits. Is something similar happening here, and does it have any effect on recording quality? Thanks.
It’s not unusual for the Audacity recording sliders to max out and freeze when they see a digital connection. The theory goes that if you have digital overload and harsh clipping damage, all the slider is going to do is give you lower volume digital overload and harsh clipping damage.
You have to solve the clipping damage between the analog presentation and digital conversion, in this case at the turntable.
Overload damage doesn’t delete numbers or mess with the digital scheme. If you screw up, it just stops following the music. The system increases digital values normally until it just runs out of numbers. The music may get louder, but all the bitstream does is go 100%, 100%, 100%, 100%, 100%, 100%.
On the timeline, that can look like somebody took a sharp blade and shaved off the tops and bottoms of the blue waves. That’s where “clipping damage” comes from.
Why did you give up the older legacy system? That’s the way you’re supposed to do it. Carefully tailor the analog signal so it’s perfect in every possible way, and then digitize it.
There’s a Promotion and Publicity level to this, too. Your older system was probably good quality so you can use it for years with good success and then leave it to your kids, right? What are you going to do with your USB turntable when the last record goes through? Put it in the trash. These turntables were designed to go into the bin, and sometimes that’s the quality you get. They fail before the last record.
Koz
I put mine in the bin very early on in my LP/45s transcription digibitting project (actually it sold it on cheaply yo a less-discerning mate).
The electronics were reasonably OK but the transport and arm/cart were rubbish - the platter was plastic and extremely lightweight and gave readily discernible wow&flutter - every now and then one of those early transcriptions pops up on the shuffle and I think ARGH!
Peter.
I didn’t. I’m asking for someone else.
I’ve read that digital volume works by truncating bits. Is something similar happening here, and does it have any effect on recording quality?
I’ve read that digital volume works by truncating bits. Is something similar happening here, and does it have any effect on recording quality?
It’s done by multiplication (or division). With floating point it doesn’t hurt anything.
But with integer audio data, yes you’re loosing resolution. If you multiply by 50% (-6dB) the most significant bit isn’t being used so with 16-bit audio you’re only using 15-bits. Still 15-bit digital is better than analog vinyl and if you have a 24-bit ADC it’s just not an issue at all.
I don’t know if the Windows recording volume control is integer or floating-point… Usually it doesn’t work at all with digital sources.
Digital recording levels aren’t critical as long as you avoid clipping of the ADC. That means you have to control the analog signal into the ADC.
Now, I’ve run into a situation where recording is being done from a 16/44 USB turntable with no gain control. Setting recording levels is accomplished using Audacity’s recording level slider typically set near to 70%.
Like I said, usually the recording level control doesn’t work with USB sources, but it should be at 100%. If the ADC (built into the turntable) is clipping, reducing the digital level after it’s clipped won’t fix it (but it will “hide” the clipping from Audacity.)
Thanks. Sounds like, even with a 16-bit ADC, you can go to “70%” on the slider and still have more than enough dynamic range to capture vinyl.