Subject:EFFECT OF ADJUSTING RECORDING VOLUME ON SOUND QUAL

Posted by: vinylcafe

Date:7/8/2015 10:00:08 AM

I'm boosting recording volume by 6 dB for transcribing vinyl to digital and wonder what effect this has on distortion/ sound quality vs. recording at 0 dB boost. Output from moving coil cartridge/ phono preamp is 250 mV so volume is significantly lower than normal CD output (1 to 2 V).

Subject:RE: EFFECT OF ADJUSTING RECORDING VOLUME ON SOUND QUAL

Reply by: Geoff_Wood

Date:7/8/2015 10:50:32 PM

To take full advantage of the bit-depth you are recording at, peaks should approach 0dBFS. This is critical if 16-bit, but no so important at 24-bit, though I would be concerned if peaks were lower than (say) -20dB. You voltage difference you have is some 18dB from the figures you gave. May be worse in the real world.

If your volume boosting is analogue domain, good. If not (ie signal is being converted to digital and then boosted by the card/driver) , then that is not so good, and no different to increasing the gain in SF, but is probably done in a cruder manner in the card !

Hard to actually know how the card is actually boosting though...

geoff

Subject:RE: EFFECT OF ADJUSTING RECORDING VOLUME ON SOUND QUAL

Reply by: musicvid10

Date:7/9/2015 9:57:34 AM

Your meters are everything.
Analog voltages are meaningless past the input preamps.

Subject:RE: EFFECT OF ADJUSTING RECORDING VOLUME ON SOUND QUAL

Reply by: Chienworks

Date:7/9/2015 2:49:05 PM

I'd say it's still very important in 24, or even 32 bit (if you have such a thing). Your analog stages are all subject to noise. Each stage should be set to its best signal-to-noise ratio level. If any stage is lower than this then you end up reducing the S/N ratio. Encoding at 24 bits isn't going to help this any more than 16 or even 8 bits.

Subject:RE: EFFECT OF ADJUSTING RECORDING VOLUME ON SOUND QUAL

Reply by: Geoff_Wood

Date:7/10/2015 2:42:13 AM

32 ? There is no such thing in an A-D converter. Even 24 bit A-D cannot acheive anything near the theoretical capability of the word-length..

If you cannot get the voltage high enough to get a full-range signal out of a AD, then the only way to increase it 'post-conversion' is to apply digital gain, which increases quantisation noise level, which is worse that any noise increase you'll get in the analogue domain unless a reallyhorrible noisy preamp/mixer/whatever.

geoff

Subject:RE: EFFECT OF ADJUSTING RECORDING VOLUME ON SOUND QUAL

Reply by: Chienworks

Date:7/10/2015 5:47:59 AM

Well, we had some 32 bit converters in some of our audio test equipment at the factory, but i do agree it's not going to be seen in consumer equipment.

And yes, that was my point exactly. You need appropriate analog levels before going into the converter, regardless of the bit depth. Vinylcafe didn't mention where he was doing the boost.

This is pretty much exactly the same topic as digital zoom for photo/video. It's absolutely senseless to do this after the conversion as you can achieve the same thing, usually better, by cropping after the fact, but it's still not as good as doing an optical zoom to begin with.

Subject:RE: EFFECT OF ADJUSTING RECORDING VOLUME ON SOUND QUAL

Reply by: musicvid10

Date:7/10/2015 8:34:37 PM

Approaching 0dBFS when recording is risky because of a little nuisance called "intersample peaks."

Subject:RE: EFFECT OF ADJUSTING RECORDING VOLUME ON SOUND QUAL

Reply by: Geoff_Wood

Date:7/12/2015 6:44:50 AM

That's why you don't do more than approach it. "approach" not meaning -0,1dB !

geoff

Subject:RE: EFFECT OF ADJUSTING RECORDING VOLUME ON SOUND QUAL

Reply by: musicvid10

Date:7/12/2015 7:07:20 AM

-1 to -3 dBFS peaks in the studio, -3 to -6 in the field are usually safe.

Subject:RE: EFFECT OF ADJUSTING RECORDING VOLUME ON SOUND QUAL

Reply by: vinylcafe

Date:7/16/2015 10:59:08 AM

To answer your question as to where the boost is occurring.......I wish I knew! How does the volume adjustment in SF10 work? Before or after the signal is digitized? If it's boosting digitally, I would consider increasing the output of my phono pre-amp or change to a higher output cartridge (currently using a Sumiko Blue Point cartridge @ 2.5 mV with Graham Slee Revelation M phono @ 40 dB that recommends input range of 2 to 10 mV).
I'm recording 16 bit/ 44k in SF10 on a desktop pc w/ Windows 7 and Juli@ soundcard.
Sorry for delay in reply, this is my first foray into SF10 forum. Appreciate all your answers!

Subject:RE: EFFECT OF ADJUSTING RECORDING VOLUME ON SOUND QUAL

Reply by: Chienworks

Date:7/16/2015 1:05:11 PM

Sound Forge has no way to affect or adjust incoming or outgoing volume. The function just doesn't exist in the software at all. The only adjustments you can make in Sound Forge are while editing, so these are obviously all in the digital domain.

If your computer has an input volume adjustment, and it should, generally this is controlling the gain into the sound card. If you have a good quality expensive card then it's probably adjusting the analog stage before conversion. If you have a cheaper card or are using what's built into the mother board then it may be doing a digital gain after conversion. The description of the Juli@ card doesn't really answer that question, but it seems to be in the higher grade ilk. Assuming you're using the -10dBv inputs you should be trying to hit peaks of 700 to 1000mv on the lines going in to the card, but i don't know how you'd measure that without some appropriate test equipment.

In any case, you should be going through a preamp/integrated amp/receiver with a Phono input connection, and then use the recording line out from that to go into the sound card. That should give you a useful level. Then adjust the input gain for the Julia@ card either in it's own control panel or in Windows recording sound mixer so that the meters in Sound Forge peak above -6dB at the loudest points, but probably not above -1.5dB in order to leave some room for transients.

If you're connecting the output from the turntable directly to the sound card then you're going to get an extremely low signal, and also one that hasn't been corrected for the RIAA curve, so the EQ will be way out of balance. In other words, don't do that! ;) Make sure you have an amp in between.

Subject:RE: EFFECT OF ADJUSTING RECORDING VOLUME ON SOUND QUAL

Reply by: ChristoC

Date:7/16/2015 3:52:59 PM

Looking at you original post, you seem to be suggesting you are needing to boost your recording by around +6dB to get a good healthy level (i.e. you are recording with peaks hitting no higher then -6dB).
In my opinion you already recording at close to optimum level, and unless you go to additional expense of different analog RIAA pre-amp (soundcards usually don't have any analog level control, just digital), if you want more level you need do nothing more but add +6dB or thereabouts digitally; this is very easily achieved in SF with barely any perceptible disadvantages in the real world (considering your source is vinyl, which by definition is already the most noisy and distorted link in the chain).
The best ways in SF for this
- if you already know the amount of boost you need: Menu|Process|Volume tool.
- if you don't already know the amount of boost you need: Menu|Process|Normalize tool.
In either case, leave a little headroom between your highest peaks and 0dB.

Subject:RE: EFFECT OF ADJUSTING RECORDING VOLUME ON SOUND QUAL

Reply by: vinylcafe

Date:7/17/2015 7:53:04 AM

Thanks all for your insights! I'll look at controlling software for the Juli@ soundcard to boost analog input; and if that's not an option, boost a couple of other recordings (volume or normalizing in SF10) to compare sound with un-edited recordings. I'm planning to digitize at least 100 of 300 lps and would like playback levels (and sound quality) to be comparable with existing recordings on my music server.

Subject:RE: EFFECT OF ADJUSTING RECORDING VOLUME ON SOUND QUAL

Reply by: musicvid10

Date:7/18/2015 7:59:11 PM

"Looking at you original post, you seem to be suggesting you are needing to boost your recording by around +6dB to get a good healthy level (i.e. you are recording with peaks hitting no higher then -6dB).
In my opinion you already recording at close to optimum level, "

---

+1

Especially if one is recording 24/96 and delivering 16/48, there is more than enough headroom to prevent loss of bit depth in the master.

Especially in field recording, that 6dB "safety net' can mean the difference between a professional recording and crap (bands tend to crank it up when the show opens).

Actually, I'm even a little more conservative than that. Since I record piano recitals I set my cap at -6dB with limiting. Sounds quite a bit better than 0dB with splatter.

Our recording capabilities far exceed practical SNR by a mile these days, so why bother trying to fill the top 6dB when it can best be used to capture the unexpected?