M2tech Young Dac and USB Cables.

[Liam]

Quote from M2tech Base Knowledge USB and Audio Doc. here http://www.m2tech.biz/knowledge.html

 

"An alternative to isochronous mode is the bulk mode, when the host may use almost all the available bandwidth to transfer data to the device. This means up to nearly 480Mbps on a 2.0 compliant port. This is quite enough for high resolution audio, far beyond the 192kHz limit. The bulk mode is difficult to use as there’s no audio USB interface IC which can use it. The only way is to use a generic USB 2.0 device interface IC and program it to handle a streaming connection using bulk mode. This also required specific drivers. The development effort is relevant and the use of a device based on bulk transfer is not very easy, but the results are outstanding. In bulk mode, there’s no timing control by the user: it only sends data when it wants or when the device require them. This leaves to the developer freedom to handle the transfer timing by the device side, rather than by the host side as happens with the isochronous mode. The device can be provided with very precise clocks and, being the master in the transfer, virtually isolates the latency variability from the output timing. An interface using bulk mode with a precise local clock may achieve extremely low jitter. Another problem related to USB is the fact that the device is often bundled to the host’s ground potential. Also, it often uses the USB 5V supply, which is also very poorly regulated and carries a lot of digital noise. One thing must be understood, anyway. The bad quality of the “USB sound” cannot be due to the poor quality of the USB 5V supply itself. Somebody says that the jitter on an USB transfer is due to the noise on the bus and that, for this reason, an USB audio device will never give high performance. That’s not true. We can transfer audio data on an USB bus in bulk mode obtaining a very low jitter, regardless of the quality of the USB port supply. The ground noise is another story: decoupling the USB interface ground form the device ground (by means of magnetic or optical isolators) is a good practice. M2Tech devices all work in bulk mode and all have outputs which are galvanically isolated from the host ground. The bulk mode allows for data transfer rates up to 192kHz (hiFace and hiFace Evo) or even 384kHz (Young)."

 

A next step for me is considering, given the description above of the M2tech Young Dac's USB interface, if a different USB cable from the stock one might improve the sound, which I am already very pleased with. Let me say that I am disposed to accept that cables can make a difference, and therefor if you disagree that's not the opinion or information I am looking for here.

 

I really wish to have the experiences of those who have tried different USB cables on the M2tech Young specifically given that the designer has taken a number of steps to optimise the interface already. As a by the way the Young is powered by the Palmer battery supply.

 

Thanks and looking forward to your experiences primarily.

[Purite Audio]

Tried a couple of different cables, couldnt hear any difference and frankly can't see how they could make a difference.

Keith.

[Liam]

Hi Keith,

 

Thanks for relating your experience. M2tech have certainly covered a number (perhaps all?) of the desirable bases in the Young USB interface. I have still wondered though if the specification and configuration of the cable might still play some part. Were any of the "Audiophile' cables included in your listening?

[1audio]

Bulk mode is not isochronous and does not have priority. Another buss request can knock the audio stream right off for a moment. Audio is usually isochronous which means in USB that it has a higher priority and the bus has reserved bandwidth for the audio. Any other activity must wait for the audio stream.

 

A bulk mode device would tend to be more sensitive to system loading and activity since its treated as non time critical data. That could make it more sensitive to stuff like cables but its just speculation. A UAC2 asyncronous interface is less sensitive to buss activity and is fully architected to work similarly to a PCI interface with buffers at each end. The older adaptive USB audio interface is sensitive to many things in the computer because it derives the clock from the average of the data transfers, a not very precise way to get there.

[Purite Audio]

Liam Hi, yes two 'audiophile' cables absolutely no difference and why would there be!

KR Keith.

[Liam]

Thanks Demian. I am very close to or possibly completely in over my head here, but I have done some reading since your post in an effort to learn. Bulk mode is the method used for transfer over firewire and it seems more accepted that firewire cables don't affect sound quality in audio applications. If I have understood correctly M2tech are using a combination of bulk mode transfer over USB and an asynchronous input in the Young dac. Is this the best of both worlds in eliminating (reducing?) the influence of the USB cable, coupled with the measures taken by M2tech to galvanically isolate the the host ground from the dac? The only other demand on the USB bus I am using in my Mac Mini is the IR and I have disconnected that. From this https://hifiduino.wordpress.com/2011/02/05/bulk-transfer-mode-in-musiland-monitor-devices/ it seems as claimed by M2tech that there is plenty bandwidth in bulk mode for hi res music, and the opinion of the poster in "some observations' is that bulk mode transfer in USB should also make a device less sensitive to cable length or other 'issues'.

[Liam]

Liam Hi, yes two 'audiophile' cables absolutely no difference and why would there be!

KR Keith.

 

That's good to know Keith. My reply to Demian may help to show where I am on this. In general, from my own experience, everything and anything can affect audio reproduction in a revealing system. For example I applied and removed ferrites from the supplied USB cable serving the dac, as I perceived they detracted from the sound, whilst I left them in place on the firewire cable from the external HD. While trawling the forum before my post here I came across a quote from Gordon Rankin that ferrites on a particular USB cable caused errors, so perhaps data can be corrupted and the device possibly still work without glitches, but sound may be affected. I like to keep an open mind and try things. In this case though with the measures taken by M2tech in the Young dac it may be impervious to cable issues, excepting possibly the outside influence of ferrites on the supplied cable

[Julf]

it seems as claimed by M2tech that there is plenty bandwidth in bulk mode for hi res music, and the opinion of the poster in "some observations' is that bulk mode transfer in USB should also make a device less sensitive to cable length or other 'issues'.

 

Yes, there is some truth in both claims, but... To quote "USB in a Nutshell" at beyondlogic.org:

 

"Bulk transfers can be used for large bursty data. Such examples could include a print-job sent to a printer or an image generated from a scanner. Bulk transfers provide error correction in the form of a CRC16 field on the data payload and error detection/re-transmission mechanisms ensuring data is transmitted and received without error. Bulk transfers will use spare un-allocated bandwidth on the bus after all other transactions have been allocated. If the bus is busy with isochronous and/or interrupt then bulk data may slowly trickle over the bus. As a result Bulk transfers should only be used for time insensitive communication as there is no guarantee of latency."

 

So bulk transfers have error checking and re-transmission, guaranteeing the transfer is bit-perfect and jitter-free. Unfortunately it is unsuitable for real-time transfer because of latency issues. So it can't be used in the usual "player software sending data in real time to the DAC" scenario - but requires your computer to act like a bulk device (hard disk or NAS), and have the DAC actively fetch the data from the computer.

[Julf]

I like to keep an open mind and try things.

 

Keeping an open mind is a good thing - but you have to make sure that the differences you perceive when trying new things are real and not caused by perceptual factors. Double-blind / ABX testing seems, despite not being perfect, to be the best tool we have for that.

[Trappistmonk]

Liam Hi, yes two 'audiophile' cables absolutely no difference and why would there be!

KR Keith.

 

I can't even tell the difference between USB and optical connection from my Macbook (running iTunes) into my BelCanto C5i ... sometimes I think I have a very bad hearing.

 

But great point on double blind testing. It is the only way to tell if you can tell the difference and I could not. Even tough I would have like to.

[Liam]

Yes, there is some truth in both claims, but... To quote "USB in a Nutshell" at beyondlogic.org:

 

"Bulk transfers can be used for large bursty data. Such examples could include a print-job sent to a printer or an image generated from a scanner. Bulk transfers provide error correction in the form of a CRC16 field on the data payload and error detection/re-transmission mechanisms ensuring data is transmitted and received without error. Bulk transfers will use spare un-allocated bandwidth on the bus after all other transactions have been allocated. If the bus is busy with isochronous and/or interrupt then bulk data may slowly trickle over the bus. As a result Bulk transfers should only be used for time insensitive communication as there is no guarantee of latency."

 

So bulk transfers have error checking and re-transmission, guaranteeing the transfer is bit-perfect and jitter-free. Unfortunately it is unsuitable for real-time transfer because of latency issues. So it can't be used in the usual "player software sending data in real time to the DAC" scenario - but requires your computer to act like a bulk device (hard disk or NAS), and have the DAC actively fetch the data from the computer.

 

Thanks for your input Julf. It seems though that M2tech have taken steps to minimise or eliminate possible adverse effects of using bulk mode, and in addition, as recommended for a dedicated system, I have turned off all but necessary applications in the headless Mac Mini, and avoided other demands on the USB bus used for music. Furthermore I use Audirvana + player, which operates in full memory mode, as described here http://audirvana.com/?p=24 and in this paper http://www.amr-audio.co.uk/large_image/MAC%20OSX%20audio%20players%20&%20Integer%20Mode.pdf, which discusses the importance of the player in audio reproduction. In all of these circumstances the expectation would be surely that the data should arrive at the dac intact and with minimal or no interruptions, which the buffer in the M2tech would cushion in any event. With no appropriate technical qualification these seem reasonable conclusions to me.

 

However, I wonder if it is still possible for the USB cable to influence the result, depending on its performance with regard to such things as impedance matching, EMI, RFI, dielectric used and configuration/metallurgy of the wires within. Keith did not notice any difference in USB cables tested with the M2tech Young dac and this is encouraging, though I perceived a difference when I applied or removed ferrites from the stock USB cable; having them on being perceived as adverse, though I was disposed to hearing a benefit. Putting them on the Firewire cable from the external HD was perceived as either negative or beneficial, I can't remember, and they are still in place.

[Liam]

Keeping an open mind is a good thing - but you have to make sure that the differences you perceive when trying new things are real and not caused by perceptual factors. Double-blind / ABX testing seems, despite not being perfect, to be the best tool we have for that.

 

Agreed. Sometimes I find though that perceived differences resulting from tweaking are either not immediately understood or are misunderstood and a week later are reversed, often due to a feeling that the music is just not as enjoyable. Such are not very amenable to double-blind/ABX testing as regards assessing benefit or not, but that is another matter.

[Julf]

Liam,

 

Thanks for your input Julf. It seems though that M2tech have taken steps to minimise or eliminate possible adverse effects of using bulk mode

 

Are you really sure M2tech really use bulk mode? I see no mention of that in the specs of the Young DAC, and as I stated, it would require the PC to work in bulk mode too, so the driver would have to fool the player software to think it is writing an USB stream, but instead the data would have to be buffered by the driver, and served out as batch transfer blocks to the DAC.

 

I have turned off all but necessary applications in the headless Mac Mini, and avoided other demands on the USB bus used for music. Furthermore I use Audirvana + player, which operates in full memory mode, as described here http://audirvana.com/?p=24 and in this paper http://www.amr-audio.co.uk/large_image/MAC%20OSX%20audio%20players%20&%20Integer%20Mode.pdf, which discusses the importance of the player in audio reproduction. In all of these circumstances the expectation would be surely that the data should arrive at the dac intact and with minimal or no interruptions, which the buffer in the M2tech would cushion in any event.

 

If the M2tech really uses bulk transfer, none of that would matter as long as the player software was bit-perfect. The software would only "play" into a memory buffer, and the M2tech would fetch data as needed in block transfer packets, checking each packet for corruption, and asking for retransmits if needed. Thus neither the cable, or the player software, or load on the USB bus, or jitter, would affect the transfer. Basically your DAc would be playing the data as if from an USB stick or a disk.

 

However, I wonder if it is still possible for the USB cable to influence the result, depending on its performance with regard to such things as impedance matching, EMI, RFI, dielectric used and configuration/metallurgy of the wires within

 

No, not if block transfer is really used.

[Liam]

Thanks Julf. That's really very helpful. Well as regards if the M2tech uses bulk mode that was my understanding of what is said in their 'Base Knowledge' document, part quoted in my OP, and with link to the whole document. You are right that no mention of this is made in the M2tech manual specs, except to confirm that the dac operates in asynchronous mode. If you can confirm my interpretation was correct, then I should have nothing to concern myself further with regard to cables, with this dac and Audirvana+.

 

Edit: Actually Julf on reading the 'Base Knowledge' doc again I see from the last sentence that bulk mode is confirmed for all M2tech dacs.

[Julf]

Well as regards if the M2tech uses bulk mode that was my understanding of what is said in their 'Base Knowledge' document, part quoted in my OP, and with link to the whole document.

 

Seems the information is a bit conflicting. On one hand the 'Base Knowledge' document states "M2Tech devices all work in bulk mode", but on the other hand the Hifiduino page on Bulk Transfer you also liked to states "it appears the Musiland device is the only “hifi” consumer USB device that uses bulk mode transfer. Other notable devices including the highly acclaimed M2Tech use Isochronous-asynchronous transfer mode", implying M2Tech does not use bulk mode.

 

Hopefully somebody who knows for a fact if the M2Tech DACs use bulk mode will chime in...

[Audio_ELF]

The Well-Tempered Computer look at the Human Audio Tabla Pico...

 

Human Audio Tabla Pico US $579 / €380 (including 27% VAT)

 

USB to SPDIF converter using Hiface EVO drivers (bulk mode).

[Julf]

The Well-Tempered Computer look at the Human Audio Tabla Pico...

 

Ah, and even better, they have the M2Tech Young on the list of DACs using bulk mode. OK, only downside is you need a special driver - so nothing for us Linux geeks.

[Purite Audio]

M2Tech are using the Xmos chip (I believe) in the new HiFace 2 which is Linux compatible, I believe they will be implementing it throughout the range soon

Keith.

[Julf]

Keith,

 

M2Tech are using the Xmos chip (I believe) in the new HiFace 2 which is Linux compatible, I believe they will be implementing it throughout the range soon

 

Great news - but will the Xmos chip use bulk transfer too?

[Liam]

Seems the information is a bit conflicting. On one hand the 'Base Knowledge' document states "M2Tech devices all work in bulk mode", but on the other hand the Hifiduino page on Bulk Transfer you also liked to states "it appears the Musiland device is the only “hifi” consumer USB device that uses bulk mode transfer. Other notable devices including the highly acclaimed M2Tech use Isochronous-asynchronous transfer mode", implying M2Tech does not use bulk mode.

 

Hopefully somebody who knows for a fact if the M2Tech DACs use bulk mode will chime in...

 

I just did a check on the date of the Hifiduino page and it was 2011/02/05, which Keith may confirm was just before or around the time the M2tech Young dac was launched, so the information about it was most likely not available at the time.

[Liam]

I have found this discussion very informative and wish to thank everybody who contributed, particularly Julf who spent most time responding and helping me to tease out the fundamentals involved. It seems to me now that M2tech have done an excellent job in addressing the pitfalls of USB music transfer and I can see no reason to spend lots of money on a USB cable with this dac anyhow.

[Julf]

We Aim To Please!

[The Computer Audiophile]

We Aim To Please!

 

I love it Julf!

 

http://www.youtube.com/watch?v=_wsoyjGrPBc

[Alan Brown]

I've had a Young for 18 months, and run it with a nice little linear power supply (which is a really worthwhile addition).

 

When I first had it, keen to maximise performance, I trialled three USB cables (well four, counting the stock cable/parts bin printer cable). These were a Wireworld Starlight, a LAT cable (some cryo-treated thing) - both at around £100 GBP. I also had some budget £30 jobbie.

 

To be concise, there was precisely no difference I could hear in my system between these cables. I was initially disappointed but soon got over it, returning all the cables for refunds...

 

I am no cable sceptic; this is the first time cables have been a non issue anywhere in my system, including digital cables - previous USB DACs, CDP > DAC over S/PDIF, all made differences. But not so with the Young.

 

I was able to detect differences with software players though, and have stuck with Audirvana+ which I considered the nicest SQ at any price.

 

Keith (or anyone for that matter) - will M2Tech be retro-fitting the XMOS USB 2 receiver chips to existing Young DACS? That would be most interesting to know.

[Liam]

Thanks for chipping in Alan. That's also good to know. Happy days