You say you leave some headroom on your mixes (v cool!) but are you worried that back at their hotel or managers office the unmastered mix wont be quite as loud as a finished CD they might compare it to?
Do you send clients out with a 'hot' DIY mastered version - perhaps a lil L2 squash so it's the same ballpark level.. ?
Do you coach them 'this is unmastered so might not be as loud as CD's you compare it to"?
A friend from NY was saying that it's got to the stage that NY A&R cant make a decision unless it has gone through the mastering process.. So they indulge in this luxury.. Are you finding that to be true..?
