Minor headphone hiss, dp24 and 2488 neo

[Scott Tribbey]

I have noticed that both the dp24 and 2488 neo have a minor but audible hiss in the headphone output. The hiss is constant regardless of the monitor level so it's not in the signal. It's likely in the output stage of the headphone amp. Both units have a seemingly identical hiss level and I imagine their headphone amps are probably the same design so it's not really a surprise.

As I only picked up both units in the last couple days I just want to make sure this is a well known "feature". It's of little consequence so long as it's not in the recording. It's makes it slightly harder to determine low-level noise in the actual signals but it's pretty subtle.

 

[Eric Guicherit]

You may want to check the build in guitar effects. These add quite some hiss in the phone output. Especially the reverb section. I stopped using these and now use separate effects modules.

 

[Scott Tribbey]

No, this is even present on a default, newly created song with no effects. Again, the effect is subtle. If you put in good headphones in a quiet room before switching the dp24 or 2488 on, then listen when you start up the machine you'll notice a slight hiss that comes in when the system starts up.

I've heard the guitar effects hiss which is considerably more noticeable depending on the effect. Still, any noise like this is early in the signal chain and so it will get louder as you turn up the monitoring volume.

The hiss I'm talking about is constant regardless of monitoring volume. In fact the noise doesn't even start up immediately. The headphones are dead silent as the system boots and then right at the end of the boot sequence, the hiss pops in. You can even hear it drop out for a fraction of a second when changing songs.

I assume the system software disables the output mute circuit only after completing boot and it gets enabled momentarily when switching songs.

 

[Phil Tipping]

My dp-32sd also has a low level hiss - think there was a thread about it on this forum some time ago. As you say, it seems to be a problem with just the headphone amp. Interesting that the neo also has a similar hiss... you'd think they'd try and address these issues before bringing out a new model.

 

[Scott Tribbey]

Thanks for chiming in Phil. I searched for a thread on it and didn't find one. It's certainly not a big deal but I've heard much quieter headphone amps even in cheaper equipment.

 

[Phil Tipping]

No problem Scott. Just for the record, here are a couple of threads I found - not obvious as they were just passing comments, but they do confirm you are not alone post #5 & post #1

 

[Mark Richards]

My DP-24 was purchased new in 2013. I'm using firmware version 1.16.

I've never noticed any hiss in the monitor circuit, but out of curiosity, went looking for it.

I listened with an AKG K701 open-back reference headphone, a SONY MDR-V6 tracking headphone, and an Audeze Sine planer magnetic audiophile headphone.

With the master stereo fader at "0" hiss was barely audible with the monitor pot set full right.

So a bit more investigation indicated that there is audible low level white noise present when the master stereo fader is at -5 or higher, and the monitor pot is at the 3 o'clock position or greater.

From a practical perspective this seems not to be much of an issue. The hiss is so low that the dynamic range of virtually any music will mask the hiss if it were making it onto the recording. And if I were to monitor with the monitor level at 3 o'clock or higher, I'd go deaf in about 5 minutes.

 

[Phil Tipping]

That's interesting Mark. This is definitely quiescent noise with the monitor knob and stereo fader both fully down. It's present with my 3 headphones: beyerdynamic DT770 250 ohm and 600 ohm, and Sennheiser HD-650 300 ohm. It is very low so normal music levels swamp it, but when you're critically listening in a quiet environment and the music fades to a hiss instead of absolute silence, you start worrying about the rest of your recording chain

 

[Mark Richards]

Hi Phil. I was looking in the other direction (everything up). Some days I can hear the hiss; other days not. (Must depend on the degree of my allergy congestion?)

I take your point about "fade to hiss".

But I wouldn't worry about the rest of the recording chain, as it seems the DP headphone circuit isn't as quiet as the rest of the DP circuitry.

For what it's worth my relative measurements (Test Gear 0 dB = .775v) of the monitor circuit after a factory reset show:

With DP-24 ON and Test Gear attached to DP-24 Left Monitor Out RCA jack:

• DP-24 All Faders/Monitor Knob Full Off: -90 dB (the stated S/N spec in the owner manual)
• DP-24 All Faders/Monitor Knob Full On: -90 dB

With DP-24 ON and Test Gear attached to DP-24 Headphone stereo 1/4" phone jack using a stereo-to-mono 1/4" patch plug:

• DP-24 All Faders/Monitor Knob Full Off: -82 dB
• DP-24 All Faders/Monitor Knob Full On: -82 dB

(Consider all the above "very likely", since mine isn't the most expensive test gear.)

My pseudo-mastering room's ambient noise floor is 27 dB (about the level of a very quiet whisper; approaching the noise floor in professional recording studios).

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For others who may read this and be less familiar with these things:

The 8 dB difference in the noise floor of the monitor out circuit v the monitor headphone circuit could be the source of the barely audible hiss when monitoring with really good headphones. TASCAM could have made the headphone circuitry as quiet as the rest of my DP-24's circuitry, but apparently chose not to do that.

However,

• The noise floor (input/record/playback signal-to-noise ratio of the throughput chain) for my DP-24 is -90 dB (per specs) - that's really good for almost all situations. My DP-24's circuitry will be 90 dB quieter (lower) than the music I process with it.

• As Phil said earlier in this thread, the very low hiss isn't going into the recording itself; it's only in the headphone circuit.

• When played over speakers, any noise in the recording lower than a quiet whisper (27 dB) will be masked (hidden) by the ambient room noise of my mastering room. This masking would be even greater in the typical home listening environment that will have higher ambient noise levels.

• When listened to using very good headphones, if there is noise in the recording below -82dB, it could become evident in a complete fade out at the end of a song when listened to using playback equipment with a noise floor lower than -82 dB.

IMO, though, even if the headphone circuit's very low level (-82 dB) hiss masks lower noise in one or more of the mic or instrument inputs that could end up in the recording itself, for all practical purposes, it's not worth worrying about. The dynamic range of virtually any music will mask the noise if it were making it onto the recording, and in most cases, a "fade-to-noise" wouldn't be noticeable until the very last millisecond of the song, if at all, at -82 dB or less.

 

[Scott Tribbey]

Thanks for the measurements Mark. As long as it's just the headphone amp, it's certainly not much of a real problem.

 

[musicianvw]

any way to fix the hiss trying other headphones? external headphone amp?? anyone have any more suggestions? thanks.

 

[Scott Tribbey]

You could certainly use an external headphone amp connected to the monitor outs. The hiss is rather distracting with a good set of phones. I have no idea why Tascam allowed this much noise in the headphone amp. Poor design work there.

 

[Mitch Gallant]

Just read this. The DP-008 headphone out is very quiet compared to my DP-24SD
https://www.jensign.com/TascamRecorderNoise/index.html

Noise is independent of any record settings etc. As noted must be in the headphone output analog driver stage.

I've included noise results for the Stereo and Monitor outs in article.