Topic: ADI 2 PRO FS distortion while tape recording

Hello everyone,

I have the following very irritating issues that I have been trying to solve for months now:

I am converting a digital signal from my MacBook pro computer with Audirvana software via USB and sending the analog signal freom my RME to my cassette decks. When I listen to the direct signal the sound is perfect, when I start recording and monitor the audio directly from the cassette the sound is very distorted (hence the final recording is also distorted) especially for the lower notes.
This happens on all deck I have tried. I must also admit that this did not happen in the beginning only after a few months.
Please help if you can, thank you very much in advance for any suggestion.

2

Re: ADI 2 PRO FS distortion while tape recording

You most probably overload the analog input stage of the cassette deck, before the record level adjustment, so it distorts even when you turn the knob far to the left. Reduce the Pro's output level to the lowest setting of +4 dBu and turn down volume to -10 dB, then try again.

Regards
Matthias Carstens
RME

Re: ADI 2 PRO FS distortion while tape recording

To avoid overloading any recorder's input amplifier that is located in front of the volume knob and therefor not under it's control:

It's a good practice to set the volume to middle position or not far below, and do the record level adjust with ADI-2's setting.

This way you can even make the most out of the analog tapes soft saturation "headroom".

BTW: in a professional environment an input volume control setting 7 of 10 usually provides the best dynamic range.

Home equipment is a little bit different.

Using a 400Hz Sinewave calibration tone can help tp figure out what's going on.
Play with the knobs and listen for the result, distortion is clearly audible with this, with no need to listen very loud.

Re: ADI 2 PRO FS distortion while tape recording

Thanks to both and this evening I will try again but I do believe I already did all of this, but I want to make sure. The tape decks I am using are the best possible out there, with independent rec levels (never more than half way) and tape calibrations but they all have this issue so I guess it depends from the correct settings of the ADI-2. Considering that this was not happening before, I am just afraid it could be a failure of the ADI electronics.

5 (edited by KaiS 2020-02-20 17:40:02)

Re: ADI 2 PRO FS distortion while tape recording

If, as you described, the sound comes out of ADI-2 undistorted, and going through the tape recorder starts distorting even before going to tape, the likely source of the distortion is quite obvious:

The tape recorder's input amplifier (or is there something connected inbetween?) is overloaded by a too hot signal from ADI-2.


Bring up the recorder's volume control and reduce ADI-2's output, not the other way round.
It does not hurt to bring the tape recoders vol. control all up for this test.

Test your signal chain with a pure sinewave, it makes error tracking easy.

If you are using ADI-2's Line Out, plug in headphones exactly there for control.
Listening to ADI-2's headphones output would not show a broken line output amplifier, in the unlikely case.

The names of the best tape machines out there start with "R" and end with "evox". Or at least "N" and "akamichi" smile
If you tell me the exact model of the tape recorder, I can have a look into it's schematic to see if there is an input amplifier that can be overloaded.
Most tapes have one.


BTW: don't use the 5-pin DIN connector or 6.3mm jack plugs on the tapemachine. These are far too sensitive.
Use Cinch inputs only.

Re: ADI 2 PRO FS distortion while tape recording

Thanks Kais for your suggestions.
I can confirm that I have tried what all of you told me up untill now, even turning way down the output setting at +4bu (and the general volume at -10db) and raise a bit the rec levels on the deck, but nothing. The sound is still heavily distorted when I monitor the audio during the recording. If I just listen to the source trhough the deck, as aI said, the sound is perfect!
Kais, if I say I have the best, that means I really do have the best! ;-) I have a Nakamichi Dragon and a ZX-9, a Revox B216 plus many others ALL FULLY SERVICED. They all show this issue. Its like the Adi just cannot cope with these vintage decks...PLEASE HELP! Sadly I am thinking of selling the Adi if I won't find a solution soon. If I cannot record for me it is useless.

Re: ADI 2 PRO FS distortion while tape recording

I wanted to add also a very strange aspect. Even though in the general level panel the analog input is at a decent level the digital ones (SPIDF and AES) all on the left are clipping at their maximum extent.

8

Re: ADI 2 PRO FS distortion while tape recording

You mean analog output. The digital outputs always run at full level.

Are you upsamling the audio, or converting it to DSD with Audirvana?

You use a simple TS to RCA cable between ADI and tape deck?

Regards
Matthias Carstens
RME

9 (edited by KaiS 2020-02-21 01:03:48)

Re: ADI 2 PRO FS distortion while tape recording

Lot's of points.

1. If the digital input's signal triggers the ADI-2's clip indicator every some seconds, this is normal with commercial recordings.

2. The Nakamichi Dragon has no amplifier at the input that can be overdriven.
Turning the Rec. Level Control down must stop distortion in the recording below a certain point, so let's go with this one.

3. Do you have a Dolby Calibration Cassette, and possibly any type of external peak meter?

The 400Hz Dolby tone is 200nWb/m - close to the maximum magnetic level a tape can store.

The point is to establish a reference for the loudness on tape that is possible with a certain deck, without relying on the recorder's calibration that might be systematically off.
This would make you record too hot.

The recorder's internal meters can assist, but are not reliable as their calibration does not follow any real reference, and in playback often are dependent on the output level control setting.
It's not possible to see if that's true for the Dragon by a quick glance into the schematic.

3. Without a meter you can establish a reference level by listening to an already recorded tape of the same type that is undistorted.
If you now record from ADI-2 slightly quieter, is the signal still distorted?

4. If yes, there might be some strong ultrasonic content on ADI's output.
Tape is easily overloaded with ultrasonics.
Try "Sharp" as ADI-2's DA-Filter.
On the Recorder use the MPX-filter.

To measure ultrasonics you would need an Oscilloscope.

5. You say you have a clean signal while monitoring the Dragons headphones output before recording, so the problem must be in the tape record path someway.

6. Did you try to record the same music from a regular CD-Player?
Please name some music pieces you record, and the source (CD, Turntable, Streaming etc.)

10

Re: ADI 2 PRO FS distortion while tape recording

So, one goes to bed late, the other one wakes up early smile

Regards
Matthias Carstens
RME

Re: ADI 2 PRO FS distortion while tape recording

MC wrote:

You mean analog output. The digital outputs always run at full level.

Are you upsamling the audio, or converting it to DSD with Audirvana?

You use a simple TS to RCA cable between ADI and tape deck?

Ok, I did not know that they work at full level. No, the analog output is normal.
I am not upsampling and not converting to DSD with Audirvana. I obviously also tried other simple players and the issue is still there.

Yes, I am using a TS to RCA cable between the ADI and the deck.

Do you think it could be possible to send the ADI for service? That would help a lot and speed up things. I really want to keep teh ADI but I am getting worn out by this issue...

Re: ADI 2 PRO FS distortion while tape recording

I would doubt that this is an issue of the ADI. Can you try to connect the ADI to a Line/Aux input on a normal Hifi amplifier, instead of directly to the tape? Also try connecting the output of the ADI directly to its own input and then record the input with Reaper or some other software - is the signal ok?

quogglot wrote:

- like the Adi just cannot cope with these vintage decks...

There is nothing to "cope" here. The ADI does not know where the signal goes, there is no way the device input will change or even distort the output signal.

quogglot wrote:

The sound is still heavily distorted when I monitor the audio during the recording. If I just listen to the source trhough the deck, as aI said, the sound is perfect!

Does that refer to the Tape/Source switch e.g. on the Dragon? Have you checked playing back the recorded signal that ends up on tape? What kinds of tapes are you using? What's the source signal? Will the Subsonic Filter on the Dragon make any difference?

Regards
Daniel Fuchs
RME

Regards
Daniel Fuchs
RME

13 (edited by quogglot 2020-02-21 19:45:06)

Re: ADI 2 PRO FS distortion while tape recording

IMPORTANT UPDATE

I tried to record on the Dragon, on the Revox and another deck with the +4db mode and now the recordings are much much better, maybe just a little bit distorted in a few passages. Insted the problem is still strongly persisting on the ZX-9, which is why I did not try on the Dragon and Revox up untill now. I was afraid that something happen to the ZX-9 but I don't think this is the case (it just got back from service) since the problem is STILL present also on another deck fully serviced I just tested, my Technics RS-B100. So the problem is actually only on a few decks...maybe KaiS could check the schematics of these two and perhaps understand the mystery behind this issue?? Thank you again to all for your help....we are almost there!

14 (edited by ramses 2020-02-21 21:28:57)

Re: ADI 2 PRO FS distortion while tape recording

I am wondering why you do not activate auto reflevel on the ADI-2
monitor the audio directly from the cassette
and if its distorted, then simply turn down the output volume on the ADI-2 until it is not distorted anymore.

While you turn down the volume on the ADI-2 watch its display at which reference level the ADI-2 is working.
When the internal relays switch to the next lower reference level you will a) hear and b) see it in the display.

This way it should give you very quickly the information at what reference / output level the distortion disappears.

It it does not disappear then something is broken.

To validate whether ADI is broken, connect it with the same outputs and cables to something like a preamp
and check whether there is distortion.

If not then this is in the area of your tape: inputs, the tape itself and what not ..

BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub13

15 (edited by KaiS 2020-02-22 07:18:09)

Re: ADI 2 PRO FS distortion while tape recording

The ZX-9 is like the Dragon, passive (non-electronic) volume control is the first signal stage, so it is able to deal with any level you feed it.


The Technics RS-B100 has an electronic muting circuit as 1st stage, it could be overdriven with very high levels.

Distortion would be audible when monitoring "Source" (before recording) from the deck's headphones or line output too.
In this case, bring down ADI-2's output until the signal is clean.


BTW: the same is true for every other deck, if the source monitoring signal is clean, a possible problem is not located at the ADI-2.


My bet is, you're recording too hot by relying on each deck's VU-meters.

Modern music recordings have much more bass and treble than the ones at the time the decks were built.
CC Cassette Tape has it's (and tape heads have their) problems with high levels in the frequency extremes.

Do you use Metal tapes?
They can take more if the deck's rec-head does not saturate before the max. flux is reached.
I liked the ones from Fuji best at that time.

16 (edited by KaiS 2020-02-24 08:33:10)

Re: ADI 2 PRO FS distortion while tape recording

Here is a graph showing the reason why modern, bass- and treble-heavy productions do challenge recording on Compact Cassette.

The frequency response, how it is stored on tape is not linear, but equalized during record to make the best out of the possible dynamic in the different frequency ranges.
For playback the curve is inverted, so you get a more or less linear result overall.
The reason for this back and forth is, the tape cannot store the same amount of energy at every frequency.

Unfortunately this was optimized for music like it was recorded in the 60s and 70s:
No Sub-Bass at all;
Reduced, intentionally filtered overall Bass;
Mid-centric;
Low Treble energy.


The (black) curve, 3180us/70us, shows the frequency response of the Magnetic Flux, how it is stored when recording on CC.
For playback the curve is inverted for the music to come back to normal.


Bass is boosted before going to tape, therefore bass distorts earlier than midrange (blue curve).


Treble is stored with a reduced level (boosted at playback to normal again).
This curve, although a frequency response, closely resembles the saturation curve (painted red) for CC.

The amount of treble energy tape can store is quite limited, the red curve shows the saturation AFTER BEING EQUALIZER/BOOSTED UP FOR PLAYBACK, BACK TO NORMAL.
Therefore the maximum possible Flux on tape is even 2 times lower!
But the red curve is "seen from the outside" so practically relevant for setting the correct recording level.
Red is for CrO2 tape, Metal tapes can carry about 6dB more treble energy.


If you now have a look on ADI-2's Real Time Analyzer, how the frequencies are distributed in modern recordings, you can imagine why problems might occur.
Treble is the same loudness as mid range, and the Sub-Bass-band is active all the time.

https://i.ibb.co/F53YB9m/IMG-1491.jpg

I had a problem with inserting the picture, thanx Ramses for the help how to do it, see below!

17

Re: ADI 2 PRO FS distortion while tape recording

You can't, sorry. Graphics need to be loaded on whatever service or storage space outside and then linked within the post.

That said: it's an interesting note, but seriously, I can't believe I can't record distortion-free (within what cassette tape can achieve), no matter what genre and age. Will check that myself on my Sankyo STD-2500 later.

Regards
Matthias Carstens
RME

18 (edited by KaiS 2020-02-23 09:56:12)

Re: ADI 2 PRO FS distortion while tape recording

I am sure that it's possible to record on Cassette from ADI-2, I would not know any reason why that would not work.
Just, with modern music you need to record on lower levels than with old Rock 'n' Roll stuff.

19 (edited by ramses 2020-02-23 09:31:12)

Re: ADI 2 PRO FS distortion while tape recording

Kai, you need to change dl=0 to dl=1 and include the URL into the img tags.
https://www.tonstudio-forum.de/blog/ind … rum-EN-DE/

In earlier times it was not required to change it to 1.
Maybe they realized that it generates too much network traffic to allow loading a picture per default.

EDIT: ok, works wink

P.S.: and this doesn't work with every cloud like from T-Systems. Therefore I prefer Dropbox.

BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub13

20

Re: ADI 2 PRO FS distortion while tape recording

ramses wrote:

you need to change dl=0 to dl=1

Nice, thanks.

Regards
Matthias Carstens
RME

Re: ADI 2 PRO FS distortion while tape recording

If you use phones 3/4 outs for NAK IN and ADI2 XLR IN for resend recorded signal to amplifier  check loopback issues.
And check cables NAK OUT to ADI IN. RCA to Balance.

22

Re: ADI 2 PRO FS distortion while tape recording

Good hint, as record often also activates monitoring and can cause feedback loops then. But the op said that using monitoring without recording is clean (arm record or record in pause state), so this should not be the issue.

Regards
Matthias Carstens
RME

23 (edited by integra 2020-02-24 13:52:12)

Re: ADI 2 PRO FS distortion while tape recording

Guogglot,
Dual phones outputs for independent internal 2DACs signal path is activated? Page 13 in Manual.
Check page 23. Source for 3/4? Default auto. AND THIS IS not acceptable for use for this case.
For use is like 2 ways DACs switch AUTO to 3/4 in the RME menu and in the player software take outs 3/4.

Re: ADI 2 PRO FS distortion while tape recording

If during recording, the sound ins undistorted with the monitor switch set to "Source", but distorted when it's on "Tape" (on the Nakas), then it really is an issue of the tape or the process of recording to tape, and not of an overloaded line input. Is the recorded signal also distorted during playback?

Regards
Daniel Fuchs
RME

Regards
Daniel Fuchs
RME

25 (edited by KaiS 2020-02-26 00:04:22)

Re: ADI 2 PRO FS distortion while tape recording

Every theory is grey so I tested practically.


Setup:

ADI-2 Pro USB mode, source Tidal on iPhone.
ADI-2 Pro Outs set to Auto Ref Level, Hi-Power.
ADI-2 Pro Analog In (Monitoring) set to +19dB
All processing in ADI-2 Pro set to bypass.
AD and DA Filters to Sharp.


Recording:

ADI-2 Line out 1/2 to:
Nakamichi 680ZX, Rec Level 7/10, Master max.
Cassette Sony MA-X 60min, best Metal Tape available.
(BTW: CrO2 tape you would need to substract 6-8dB from all levels below!)
Azimuth, Bias and Level newly and precise calibrated, frequency response checked.


Monitoring:

680ZX Line Out to ADI-2 Pro Analog In, routed to headphone out 3/4.
Listening on STAX SR009 / SRM1-Mk2-pro (known for not distorting by itself).
Comparison done by switching Tape/Source on the 680ZX during record.


Results were as expected, typically for cassette recording:
Nothing unexpected happened.
The tape recorder behaved with RME ADI-2 Pro like it does with any other source.

Conclusion:
Source signal always was clean, even at levels way above those used.
From tape, with Dolby switched off, pulses and attacks were almost unchanged up to a recording level of -5 to 0dB (on 680ZX peak meter).
Above progressively the percussive attacks were softened, bass becomes audibly distorted above ca. +7dB at max, depending on the kind of program used.
With Dolby B attacks and brilliance were slightly reduced, so Dolby B was not used in this test.


The transition from clean to distorted is very soft, so it largely depends on personal preference at which point one would could consider the signal as distorted.
As a studio professional having started my career working with analog, but for a really long time with digital now, I am not very tolerant to distortions.
If the signal is changed, attacks washed out and punch in the bass range is compromised I don't like that.
As usual, your mileage may vary, especially with analog tape the transition  between clean and squashed is quite soft, starting ca. at -10dB ranging up to +10dB peak input level.
At that point the output has lost about 3-5dB peaks by saturation, even more in the upper treble range.



With Sinewaves the tape behaved normal too.
Max rec. Levels rel. to Dolby Level 200nWb/m:
    0dB @  33Hz / 3% K3
+10dB @ 333Hz / 3% K3
   0dB @ 10kHz Saturation Level
  -5dB @ 12.5kHz Saturation Level
-15dB @ 16kHz Saturation Level

Here it's obvious what I explained in my former posting above:
As usual with small track, slow speed analog tape, highest level can be achieved in the mid range.
Maximum clean Bass level is 10 dB lower.
Treble is saturated much earlier too, and saturation means it's already completely distorted.

This figures fit to the way music was produced at the time Cassette recording was invented, strong midrange and recessed bass and treble.
This kind of fits to vinyl discs too, which have comparable limitations.



Some details and a selection of musical examples:
Following music taken from current Tidal steaming version, that is partly different to the original CD release.

Levels:
The Nakamichi 680ZX has a frequency independent Peak Meter with an attack time of 10ms, shorter peaks are not fully shown.
Real peaks can be estimated as ca. 6dB higher than visible on 680ZX's Peak Meter.
0dB is calibrated to 200nWb/n, = Dolby Level, not very hot!


Dire Straits - Six Blade Knife:
Clean up to ADI-2 Pro Out -33dB, 0dB on 680ZX Peak Meter
Higher levels give progressively more distortion in the bass, and the percussions become softened.

Donald Fagan - Morph the Cat:
Clean up to ADI-2 Pro Out -36dB, -5dB on 680ZX Peak Meter.
Above the very peaky percussion attacks are progressively squashed, sound becomes dull.

Michael Jackson - Bad (2012 Remix):
Clean up to ADI-2 Pro Out -37dB, -2dB on 680ZX Peak Meter
With this one you can go much higher without obvious distortions, it just sounds softer overall.

Re: ADI 2 PRO FS distortion while tape recording

Check ADI setup. Just look on my posts.

27 (edited by KaiS 2020-02-25 23:46:09)

Re: ADI 2 PRO FS distortion while tape recording

integra wrote:

Check ADI setup. Just look on my posts.

Yes I did, thank you for the hint.
In USB mode those options are not available.


If you read my posting, "Setup" section, you'll see I configured two completely independent signal path's: one for recording - and one for monitoring/measurement:

1. iPhone Tidal -> USB -> DAC 1/2 -> Tape Machine Record In.

2. Tape Machine playback (via Source/Tape switch on 680ZX) -> ADI-2 Pro analog in/ADC -> DAC 3/4 headphones out -> STAX SRM1 amp and SR009 headphones.
2b. This path, ADC -> USB -> iPhone AudioTools measurement software.


This perfectly worked, no unwanted path interlink to trigger your mentioned possible feedback loop problem.

I could have plugged the 680ZX Playback Outs directly to the STAX amp.
But the way I did has been more convenient with the levels.
As I used the iPhone for the above measurements too, ADI-2 Pro even served as measurement frontend.


As one can see above, the results showed ADI-2 Pro behaves like every other DAC for feeding the tape machine.
Max. tape recording level of +10dB at 333Hz says the tape's capabilities can be fully utilized.

I see I've missed to give further explanation for those not familiar with analog tape:
Full scale level on tape is always referenced to the point of 3% distortion.
This is done because tape's transition from clean to distorted is very soft and therefore hardly audible.
Opposed to an electronic amplifier were the output power is referenced to 1% distortion, 3% reference really is the normal way to measure analog tape's data.
The result is exactly the expected value, this 3% dist. at +10dB above Dolby Level is not a fault!


So the topic starter's suspicion there might be something wrong with ADI-2 Pro could not be confirmed, at least not in general.
This would not exclude that his personal ADI might be broken, specially if he gets different results.

I'm curious to hear from him.
Hope he comes back to us.

Re: ADI 2 PRO FS distortion while tape recording

Switch to Preamp mode. Page 34.

Re: ADI 2 PRO FS distortion while tape recording

Thank you all very much. I am trying to test all your suggestions. It will take some time but I'll be back.
In any case it is very frustrating that there isn't a clear issue and solution to this situation.
Stay tuned!