Need some advice on DAC please

guylj

Standard Member
I have an audio setup which is based on an Advent 4211 netbook running iTunes into some mostly elderly Hi Fi kit - it's for casual listening not my main listening room.

The problem is that the netbook's onboard Realtek sound is plagued by background noise which is a typical laptop issue. If you run the notebook on the battery only then it quietens right down but the battery is only a 3 cell and runs down quite quickly.

My first attempt to improve things was to use a Firestone Fubar II USB DAC which gave a much improved sound (although not absolutely silent) but unfortunately had a fatal flaw which was every few minutes the USB Suspend LED flickered usually accompanied by an audible click. I tried a number of software performance tweaks to no avail and had to return it.

I had an inexpensive USB Soundblaster Connect unit sitting in a drawer and found this marginally quieter than the onboard Realtek so have been using this. Again with the notebook on battery power it's very much quieter. As this Soundblaster takes its power from the USB I guess the noise is coming through that route. Unlike the Fubar, this little box has no issues with the USB data interface - never skips a beat.

Recently it occurred to me that as the Soundblaster has an optical out connection (which I've never used) a possible improvement might be to connect this to a DAC which has both an optical input and its own power supply. After some hours Googling I came across the Beresford TC-7510 which seems like it might fit the bill.

As I am a novice at all this I wondered if anyone with experience of this type of thing might be able to comment as to whether it might be a workable solution.

There is also the Beresford TC-7520 which is a bit more expensive but which also has a direct USB connection as well as optical in. If this was at least as quiet as the Fubar II on the USB input and did not suffer from the Fubar's USB data handling glitch then there would be no need for the USB Soundblaster at all. That would by-pass any possible issues with an optical connection.

All advice gratefully received!
 

clockworks

Novice Member
I'd be tempted to go with the optical connection, as that will give you complete electrical isolation. Should fix the noise problem.

I'm currently using optical out from my iMac into an M-Audio Flying Cow DAC, via an optical to coax convertor. Absolutely silent until the music starts.
Tried a similar thing with a Windows laptop a couple of years ago. Worked OK. Sounded better when I bypassed the Windows audio drivers, using a universal ASIO driver (from foobar, IIRC).

If you can find one second hand, I'd recommend the Flying Cow as an affordable DAC. I bought one new a couple of years ago to use with my main system. Compared favourably with a much more expensive "hi-fi" DAC.
It looks rubbish (designed for semi-pro studio use), but sounds excellent.
I picked another one up last month on eBay for £45 for use with the iMac - bargain!
 

guylj

Standard Member
Many thanks for that. As the notebook itself doesn't have digital audio out I will be dependent on the USB Soundblaster to produce the optical signal.

Is the optical signal from a cheap device like a Soundblaster likely to be OK for driving a DAC do you think? I don't know how critical signal levels etc are in the optical world.
 

clockworks

Novice Member
I was using the onboard Realtek optical output from my laptop, which worked fine. Never tried a Soundblaster USB device, so can't comment on those. You shouldn't have a noise problem, though. Noise is normally generated in the analogue domain, so separating that from the PC with an optical connection will allow you to use the mains power supply.
 

guylj

Standard Member
Could I pick your brains again please? Having never used the SPDIF on my USB Soundblaster I thought I had better try to check if it is actually working OK before getting an optical DAC.

So I connected the optical cable between the SPDIF Input and Outputs. Played a WAV file on the PC and fired up some recording software and set it to use the SPDIF input. Then played back the recording.

It was fine except it was important to match the sampling frequencies. The recording program defaulted to 44.1 kHz and the Soundblaster SPDIF output to 48 kHz. I managed to download some software from the Creative site that allowed me to switch the SPDIF output from 48 to 44.1 - however it seems to prefer 48 given half a chance. So it was easier to set the recording program to 48 also. Recording a 48 signal at 44.1 gives a pitch drop and slower tempo. The creative utility also has a box for setting the Soundblaster's SPDIF input frequency (to 32, 44.1 or 48 kHz according to the manual) but this seems to be blank and disabled.

Am I likely to get a similar situation with an optical DAC? Or do they automatically detect the incoming frequency and switch accordingly? And given that the WAV files are recorded at 44.1 is it wise to let the Soundblaster upsample them to 48?

Many thanks again.
 

clockworks

Novice Member
I remember reading about this 48/44.1 problem with Soundblaster cards. It's certainly better to use 44.1 for CD-sourced material. Up-sampling to 48 must be bad for sound quality.
IIRC, that was the reason for people preferring to use non-Soundblaster cards.

I've not noticed any switches for selecting the sampling rate on external DACs. That means they either auto-select, or they only do 44.1.

This is a real minefield, isn't it!
Another reason why I switched to Mac.
 
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guylj

Standard Member
I found this statement for the Cambridge DACMagic here :-

Specifications / DacMagic Digital to Analogue Converter / Digital to Audio Converters / Products / Cambridge Audio

"Digital input sampling frequencies supported: 32kHz, 44.1kHz, 48kHz, 88.2kHz, 96kHz (44.1kHz, 48kHz for USB)"

and here :-

DacMagic Digital to Analogue Converter

"Other features include ... an incoming sampling rate indicator which shows the original source quality."

"Incoming sampling rate indicator 32/44.1/48/88.2/96kHz"

I downloaded the user manual and that shows that there is a row of LEDs indicating the input :-

"In the presence of an incoming digital stream, the relevant LED will light up to indicate the incoming
digital sampling frequency (between 32kHz and 96kHz LPCM)"

I take that to mean that it detects the input frequency automatically as there is no switch on the panel to change it.

It looks very nice but it's quite a bit more expensive than I would ideally wish to pay and I think it might be overkill for the other audio kit it would be working with.
 

clockworks

Novice Member
Looks like the DAC will auto select, as you say.
Now all you need to do is convince your PC to play back at 44.1. Maybe a better USB to optical device would do the trick. M-Audio make some suitable "sound cards".
 

guylj

Standard Member
The Soundblaster will do 44.1 kHz if you move a little switch on the side from "Digital/Analogue" to "Digital". That disables the analogue I/O but then the Creative Software gives you the option to choose between 44.1 and 48 on the SPDIF out. If you move the switch back to "Digital/Analogue" the software doesn't give you a choice and you are locked at 48.

Strange set up but yes you can force it to output SPDIF at 44.1 kHz.

A friend of mine suggested a cheaper option would be to try to find a cleaner power supply for the notebook PC!
 

guylj

Standard Member
I tried another approach. Just as a test I connected the laptop power supply via an unearthed plug. The noise just disappeared - no difference to running on battery power only.

I'd rather not run unearthed permanently though so I wondered if a Ground Loop Isolator might allow me to achieve the same results.

Maplin do a couple :-

Ground Loop Isolator > Maplin

Ground Loop Isolator > Maplin

The second one has a better audio frequency response although I guess my Ruark Swordsman Plus II 6.5" drivers aren't producing anything below 40 Hz anyway.

Does anyone have any experience of ground loop isolators in conjunction with laptop audio?
 

guylj

Standard Member
My local Maplins were very helpful. They had the cheaper isolator in stock and as it was in packaging which could be opened carefully and replaced ( in fact it looked as if someone already had done so!) they were happy for me to buy it with the option of a full refund or part payment against the more expensive Xitel isolator which they could order in specially. I landed up taking the latter course.

Both isolators were 100% effective at removing the noise when using the USB Soundblaster. I could not detect any difference between battery and mains power at any sensible volume level.

Neither isolator would completely kill the background noise when using the onboard Realtek audio chip. It was noisier than the Soundblaster without an isolator and although both isolators considerably reduced the noise there was still enough remaining to be obtrusive.

The cheaper model did quite a good job and is certainly more than adequate for car audio purposes. I did detect a slight muddiness in the bass which was noticeable on a track with jazz acoustic double bass. Similarly the mid range and treble were just a tad less clean.

The Xitel was a different beast - to all intents and purposes completely transparent in my admittedly not terribly HiFi system.

One thing to be aware of is that the Xitel comes in sealed packaging so once opened you can't return that one for a refund like you can with the cheaper model.
 

xD00Mx

Standard Member
What i'd do is Bypass the Realtek card and download Wavelab and use that as a source program to direct the sound through the Bypassed card (basically using it for the hardware but not the software) the card itself wont be that bad, but the software that runs it is designed by a total womp.
Go with the kid that said use Optical and usb if possible but do what i said if you can because it would also take toll off your ram. as it'll have an allocated amount of ram because it's 'in house' hardware. (it'll free up your machine's speed) hope this helps!
 

guylj

Standard Member
Here's an update.

Bought a CYP AU-D3 DAC for just under £40 and connected its optical input to the optical output from the Soundblaster thus removing the direct electrical audio link with the notebook PC.

I'm very pleased indeed with the results. Slightly counter-intuitively I had to remove the Xitel Ground Loop Isolator as with it in circuit there was a mains buzz. But without the Xitel there is no background noise whatsoever that my ears can detect now. Also the sound is cleaner all round with tighter bass and more detailed percussion but never tiring.

Another slightly counter-intuitive thing is that the overall sound seems to be best with the Soundblaster in its default 48 kHz sampling mode (the CYP automatically adjusts to the input sampling rate). All my audio is 16 bit 44.1 kHz and I had assumed it would be best to use that rate right through the whole system. I suspect what may be happening is that the SB automatically upsamples any incoming 32 kHz or 44.1 kHz input to 48 kHz; then if you request 44.1 kHz output (via the software utility) the SB downsamples back to the original 44.1 kHz. If I'm right that would mean an extra resampling operation which would explain the slightly worse sound using 44.1 kHz between the SB and CYP rather than 48 kHz.
 

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