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Topic: Are 'Line In' recordings being dynamically compressed on-the-fly? (Read 6677 times) previous topic - next topic
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Are 'Line In' recordings being dynamically compressed on-the-fly?

I've been transferring vinyl for digital storage. I'm not using any professional equipment here, just a desktop PC, turntable, preamp, and cable into the line in back of the PC.

When reviewing my recordings, I've noticed that some of them are flatheaded when viewing them as waveforms. And a Replay-Gain scan show many of my recordings are peaking at the same exact value. I highly doubt this is coincidence, so I believe there is something, whether its software or hardware related that's dynamically compressing or hard-limiting my recordings on-the-fly. I've checked the settings for the mic and software, turned off RealTek Audio Manager, and nothing seems to be affecting it. I'm thinking maybe WASAPI might be be the reason but I'm no expert when it comes to audio hosts. Any ideas?

Re: Are 'Line In' recordings being dynamically compressed on-the-fly?

Reply #1 –
"Are 'Line In' recordings being dynamically compressed on-the-fly?"

Quite possibly.

Lower the input gain by 10dB or so and then try again.

Re: Are 'Line In' recordings being dynamically compressed on-the-fly?

Reply #2 –
I have a bit of software called TotalRecorder which, if you use the recording wizard, allows you to play about 10 seconds (of whatever you select that sounds like the loudest bit of the record), and it adjusts the input level to suit. Unfortunately, it isn't freeware, but I'd be surprised if there wasn't something free out there that offered the same soundcheck option.

I no longer use TotalRecorder for recording, as I am more of a fan of Audacity these days (much easier to edit files than TR), but the input level settings on the former apply to the latter, so it is worth doing anyway. After recording a complete album, you can apply Audacity's 'normalise' effect, then you're ready to slice'n'dice the file into individually exported tracks.

Re: Are 'Line In' recordings being dynamically compressed on-the-fly?

Reply #3 –
At what level are these waveforms "flatheaded"? I would suspect clipping before I looked for compression, although compression was a fault of some early Creative soundcards.

In order to avoid clipping when the input level is too high, level or gain control is necessary in the analogue, before the ADC. When the input level above the max hits the ADC, clipping is all it can do.  Are there analogue control circuits on today's MB audio inputs? There aren't on professional line level inputs.

Re: Are 'Line In' recordings being dynamically compressed on-the-fly?

Reply #4 –
If the tops and/or bottoms of the records are flat after coming off vinyl, then yeah it is clipping. Clipping is essentially a very drastic form of compression (compression with an infinite ratio). But the worst part about it will be aliasing that's introduced along with the fizzy sound of the clipping.

Definitely re record it at a lower level if possible. Having the average volume be at roughly -18db should give you room for the transients (loud spikes) to come through without clipping.

Also remember that with digital, the noise floor is so low that there's no real reason to record hot in this situation. You can record at a lower volume and then raise the volume later.

Re: Are 'Line In' recordings being dynamically compressed on-the-fly?

Reply #5 –
Clipping is the worst kind of compression!  ;)

I usually check the peaks after recording (before normalizing or any other processing) and if they are hitting 0dB, I assume it's clipped and I start-over.    (For example in Audacity, the Amplify effect will default to whatever gain is required to hit 0dB, so if it defaults to +3dB, your current peak is -3dB etc.)

I usually shoot for peaks between -3 and -6dB.    Nothing bad happens when you get close to 0dB, only if you try to go over...  

-18dB might be too low for a consumer soundcard...    If the soundcard is noisy, the noise could become an issue when you boost the levels digitally.   

Re: Are 'Line In' recordings being dynamically compressed on-the-fly?

Reply #6 –
Quote from: DVDdoug on
Clipping is the worst kind of compression!  ;)

I usually check the peaks after recording (before normalizing or any other processing) and if they are hitting 0dB, I assume it's clipped and I start-over.    (For example in Audacity, the Amplify effect will default to whatever gain is required to hit 0dB, so if it defaults to +3dB, your current peak is -3dB etc.)

I usually shoot for peaks between -3 and -6dB.    Nothing bad happens when you get close to 0dB, only if you try to go over...  

-18dB might be too low for a consumer soundcard...    If the soundcard is noisy, the noise could become an issue when you boost the levels digitally.   

Thank you for all the advice so far, I'd like to mention the setting I have now, it limits to about 88% of full scale according to the Replay-Gain scan. That's where it flatheads. I did another recording at a lower level and of course, nothing is flatheading. A little disappointed that something is making it flat out like that as such a low level but, I'm gonna have to deal with it by re-recording it.

Re: Are 'Line In' recordings being dynamically compressed on-the-fly?

Reply #7 –
Quote from: DVDdoug on
-18dB might be too low for a consumer soundcard...
It might be too low for an old one.  If the card can't adequately provide 18dB of headroom and the content warrants it then I'd say it should be replaced.  It's a shame that vinyl that was sourced from heavily clippressed material will likely also require some additional headroom, but I don't know that it will come at the expense of a problematic noise floor; even at elevated listening levels so long as they are still reasonable.

Quote from: DVDdoug on
If the soundcard is noisy, the noise could become an issue when you boost the levels digitally.   
...or analog-ly ;)

Re: Are 'Line In' recordings being dynamically compressed on-the-fly?

Reply #8 –
Quote
...or analog-ly ;)
Good point.      The idea is to get a good signal-to-noise ratio.    Hopefully, the soundcard/interface is much better than the vinyl itself so it's not an issue.  

Re: Are 'Line In' recordings being dynamically compressed on-the-fly?

Reply #9 –
Quote
the setting I have now, it limits to about 88% of full scale according to the Replay-Gain scan

This setting is made -- how? Does you phone preamp have an input or output level control (very unusual but not unknown) or is this happening on the computer? If the later, what makes you believe there is analogue level control on the line level input?

If what format are you recording?

Re: Are 'Line In' recordings being dynamically compressed on-the-fly?

Reply #10 –
I had the same issue trying to record the output from a Chromecast Audio set to "Full Dynamic Range", which supplies a ~2Vrms signal. Unfortunately the line-in on my PC only accepts a maximum input level of ~1.5Vrms, so it ended up clipping.

The only solution is to attenuate the signal at the source, you cannot do anything on the PC side..

Re: Are 'Line In' recordings being dynamically compressed on-the-fly?

Reply #11 –
Quote from: powerstone05 on
Thank you for all the advice so far, I'd like to mention the setting I have now, it limits to about 88% of full scale according to the Replay-Gain scan. That's where it flatheads. I did another recording at a lower level and of course, nothing is flatheading. A little disappointed that something is making it flat out like that as such a low level but, I'm gonna have to deal with it by re-recording it.

Can you put the stream go through some metering system before recording it?
I normally use Reaper as a rec software with couple VST plug-ins in data path (level setting (Sonalksis FreeG) and metering (Voxengo SPAN)). As Reaper handles pre and post FX I can put all processing plug-ins (subsonic/gain) where I want them to be and metering system into master output channel.

Re: Are 'Line In' recordings being dynamically compressed on-the-fly?

Reply #12 –
Quote from: KozmoNaut on
I had the same issue trying to record the output from a Chromecast Audio set to "Full Dynamic Range", which supplies a ~2Vrms signal. Unfortunately the line-in on my PC only accepts a maximum input level of ~1.5Vrms, so it ended up clipping.

The only solution is to attenuate the signal at the source, you cannot do anything on the PC side..
Found similar problems with some portable recorders/ADCs. Most of them show this behaviour, they are not meant to record "high" input levels.

No way the clipping comes from vinyl as you see it, since it would appear with some phase deviation and therefore not exactly at the sampled peaks neither "flat". There are threads here related to low pass filters showing that.
https://s32.postimg.org/i9gvdhwlx/image.jpg

So provide info about what ADC are you using, or your motherboard and consider the most probable cause of your problem is you need to record at lower levels and apply gain in digital or buy a more capable ADC for your needs.

Re: Are 'Line In' recordings being dynamically compressed on-the-fly?

Reply #13 –
The normal practice when recording from any analogue source is to provide the proper level to the ADC input.  The problem with any given source may be either too low a signal level or too high a level. Once the signal is digital, certain aspects are fixed. No effects in any recording program can alter the fact that too high a signal was clipped in the ADC or that too low a signal has a poorer signal to noise ratio.

Passive resistance to lower the level is functional when the signal level is too high but can't help is the LP is recorded rather low as is not uncommon on longer classical pieces. The most common way to control both is by running the signal through a mixer. For microphone there is gain control on the microphone preamp input side and sometimes level control reduction control on the output side. . For a previously recorded source such as LP or tape, an adjustable level out, usually in a line level preamp  is needed. A mixer provides this. A HiFi preamp also works but is normally a much more expensive route. There are also some (usually on the lower end of the price scale) phone preamps which incorporate a line level preamp stage.

Different LPs have marked differences in signal level. Every variation of phono cartridge has a different output level for a fixed input. The EQ specifications of phono preamps are well defined but there are significant differences in amplification, which is rarely adjustable. If the particular LP, cartridge, phono preamp isn't a good fit to the ADC input, something else is needed between the phono preamp and the ADC.

Unless there is an adjustable analogue stage in the computer motherboard, the best practice is to adjust the level before reaching the jacks and to set whatever controls are on the computer system to maximum so the data isn't altered before being recorded. Once recorded you can play with any characteristics to your heart's content, then undo what you don't like and start over -- without re-recording.

Re: Are 'Line In' recordings being dynamically compressed on-the-fly?

Reply #14 –
Quote from: powerstone05 on
... ... ...  I'm gonna have to deal with it by re-recording it.

I'm afraid that you are simply finding out that digitizing LPs is not  a plug and play task. It takes  quite a lot of preparation, level setting in hard and software, monitoring, reviewing, followed by as many hours post-processing as you've got, unless your vinyl is miraculously perfect. i used to do quite a lot, but my work/results did not approach 5% of the real masters of this stuff.

these days my hearing is not up to the job, but, frankly, I got too lazy several years before that happened.
The most important audio cables are the ones in the brain

Re: Are 'Line In' recordings being dynamically compressed on-the-fly?

Reply #15 –
Quote from: AndyH-ha on
Quote
the setting I have now, it limits to about 88% of full scale according to the Replay-Gain scan

This setting is made -- how? Does you phone preamp have an input or output level control (very unusual but not unknown) or is this happening on the computer? If the later, what makes you believe there is analogue level control on the line level input?

If what format are you recording?

The setting is from the level I had it set on my Line In volume control, which was at 17 / 100.

My preamp is a usual cheap one from Pyle Audio, no controls on it, recording to Audacity in lossless 96K/32B float. My "soundcard" is actually built into my motherboard, a ASRock FM2 A88X Extreme6+, which is RealTek. I think it's from 2013.

Re: Are 'Line In' recordings being dynamically compressed on-the-fly?

Reply #16 –
I did another recording and the 'flatheading' is still happening even at a lower input level.

https://www.dropbox.com/s/7miyxuphs44f4yz/Screenshot%202016-05-10%2019.38.28.png
https://www.dropbox.com/s/cdxrjpde838m9fs/Screenshot%202016-05-10%2019.53.15.png

The record is from 1981, I'm no expert but I doubt the source audio was THAT compressed. It appears that the limiting is actually changing in proportion to the input level.

EDIT:
Also Replay-Gain is showing both recordings as peaking at the same exact value.

https://www.dropbox.com/s/3edt8db9dz8pbs8/Screenshot%202016-05-10%2020.07.45.png

Re: Are 'Line In' recordings being dynamically compressed on-the-fly?

Reply #17 –
This is your ADC.
http://www.realtek.com.tw/products/productsView.aspx?Langid=1&PFid=28&Level=5&Conn=4&ProdID=328

Quote
*Front-DAC with 115/110dB SNR (A-weighting, Differential/Single-End Output), ADC09h with 104dB SNR (A-weighting)
*DACs (except Front-DAC) with 96dB SNR (A-weighting), ADC08h with 93dB SNR (A-weighting)

All peaks at the same value is clearly hard limiting in digital domain and nothing to do with things before the ADC, you don't get all peaks at the same level in analogue in such perfect way no matter what you do or broke.

So... continue lowering the level before recording at line in.

Btw seeing the ADC specs I don't get how the hell you manage to clip the signal at such low level... It makes no sense at all even if you solve this lowering even more the level, recheck all windows settings or the software you are using.

SO? Software you use? WASAPI, ASIO, MME for the recording device?

I remember a similar problem via Audition CC & Asio.

Re: Are 'Line In' recordings being dynamically compressed on-the-fly?

Reply #18 –
I remember soundcards could be switched between mic or line-in mode for the same input.
Is troll-adiposity coming from feederism?
With 24bit music you can listen to silence much louder!

Re: Are 'Line In' recordings being dynamically compressed on-the-fly?

Reply #19 –
Quote from: Wombat on
I remember soundcards could be switched between mic or line-in mode for the same input.
I also suspected this but in either case (using line or mic level) the signal should not clip before 0dBFS at all. Try to uninstall the Realtek driver and Windows should automatically switch to the default HD audio driver which may solve the clipping problem (or at least let the signal clip at 0dBFS if it is a hardware limitation in input voltage).

[EDIT]
Quote
The setting is from the level I had it set on my Line In volume control, which was at 17 / 100.
I overlooked this one :D

Re: Are 'Line In' recordings being dynamically compressed on-the-fly?

Reply #20 –
It is hard to diagnose when one doesn't have any specs about the input (your line in), but the controls are most likely working in the digital domain. In that case, it should be set at maximum (100/100), with level control happening before the input (in the analogue domain).

If it is really a microphone input, that control should be a gain control for a microphone amplifier, which isn't extremely rare on a MB built-in. That isn't a proper line in and will give you inferior results. A microphone amplifier is not a good thing to follow the output of a phono preamp.

It is possible there is a zero point somewhere on that scale of 100, with attenuation below that point and amplification above it, both working on the digital, but attenuation only is the norm for real line level inputs. In the case where is does have digital amplification by Windows, its should be set at the zero (no effect) point.

My soundcard has a mixer application with level controls (not part of the Window's OS).  They only attenuate, which is the norm. Their use might be appropriate if I were recording something from multiple sources into one stereo (or mono) track, to prevent the sum from clipping, but for LP or cassette input they are always set at maximum (no attenuation).

Referring back to the information if my previous post about the signal level determining items from a TT (the LP itself, the phono cartridge, the phono preamp), you could have a signal at the ADC input that is considerably too high or one that is too low for optimum results. There have been many previous complaints on this forum (and a hundred otheres) from people trying to record LPs that frequently clipped because the combination of cartridge and phone preamp overdrives the soundcard line in (for virtually all LPs). If this happens with most of all your LPs, a simple resistor divider after the phono preamp will do the trick. If values are selected reasonably, it doesn't have to be variable.

You might also have something else set within the computer's controls, such as an AVC or hard limiter, in which case that should be disabled.

Re: Are 'Line In' recordings being dynamically compressed on-the-fly?

Reply #21 –
If you're recording using standard version of Audacity, it's pointless to use higher than 16-bit resolution.
IIRC, WASAPI in Audacity is for loop back recording only (if not improved lately) so are you recording "what you hear"? --> Try using MME/DS.
IIRC, latest Windows versions has this limiting feature but I can't recall if it's for input signal as well.

In your case, I would try other piece of recording software with Asio4All driver.
Acon's Acoustica Basic is free and supports ASIO - https://acondigital.com/products/acoustica-audio-editor/

Re: Are 'Line In' recordings being dynamically compressed on-the-fly?

Reply #23 –
Quote from: robertzombie on
Quote from: Isabelxxx on
I remember a similar problem via Audition CC & Asio.
Would you mind telling us a bit more about this?

There is not too much to say since documentations its obscure at best... and Adobe developers doesn't give any help. Just my experience.

Some Audition versions don't work properly with some ADCs via Asio, specially Audition CC. If your combination works then great but otherwise you are f***. I remember  I also tried WASAPI those times without luck.
You can use other versions of Audition or even other recording programs along ASIO and they will work ok. At some point you find that ASIO works perfectly, any other program too and the only thing failing is Audition CC for that particular ADC.

So whenever you find no config. would fix the problem, trying another program may be the solution.

Re: Are 'Line In' recordings being dynamically compressed on-the-fly?

Reply #24 –
Quote from: powerstone05 on
I've been transferring vinyl for digital storage. I'm not using any professional equipment here, just a desktop PC, turntable, preamp, and cable into the line in back of the PC.

Probably entirely adequate.

Quote
When reviewing my recordings, I've noticed that some of them are flatheaded when viewing them as waveforms.

That would most likely be clipping, and it means that you have too much gain someplace in your signal chain.

Quote
And a Replay-Gain scan show many of my recordings are peaking at the same exact value.

Hihgly unlikely unless there is local clipping.

Quote
I highly doubt this is coincidence, so I believe there is something, whether its software or hardware related that's dynamically compressing or hard-limiting my recordings on-the-fly.

Hold that thought, especially as relating to  hardware

Quote
I've checked the settings for the mic and software, turned off RealTek Audio Manager, and nothing seems to be affecting it.

That means that the clipping is taking place in hardware that either has no gain control, or has its gain control is positioned after the part of the device that is clipping.

Quote
I'm thinking maybe WASAPI might be be the reason but I'm no expert when it comes to audio hosts. Any ideas?

WASPI is unlikely to be the cause.

I'd focus on the preamp.   You  may have to totally replace it with a device that has more headroom,  and/or put some kind of gain reducing device (an attenuator) between it and the PC audio input.